http://www.ComputerBob.com/guides/lock-ups.php .
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by ComputerBob
May 30, 2000
Last Updated January 6, 2001
At least a couple of times each semester, someone asks me why their PC is locking up. Then, I ask them a series of questions, to try to figure out what is causing their problem. This article summarizes much of what I know and have experienced about why PCs lock-up, and attempts to give you some ideas for solving your PC's lock-up problems.
A lock-up occurs when the PC appears to "freeze," and both the keyboard and mouse are unresponsive. If you move the mouse, the mouse pointer on the screen stays still. If you press the Control-Alt-Delete key combination, nothing happens. The only way to get out of a lock-up is to switch off the PC, wait a few seconds, then turn it back on again.
In my experience, all of the things listed below can cause a PC to lock-up:
Microsoft Windows 95/98 is not an extremely stable operating system. Unlike the older Windows NT or the newer Windows 2000, which were designed for extremely secure and extremely stable use on corporate networks, Windows 95 was designed for unsecured stand-alone home use, as well as for maximum compatibility with older hardware and software. As a result, Windows 95 sometimes locks up or crashes for no apparent reason. Windows 98, a newer, better version of Windows 95, was built upon Windows 95's basic software architecture, so it suffers from the same lack of stability. While I can often go for several days without my Windows 98 PC suffering a crash or a lock-up, many people suffer either a crash or a lock-up at least once each day. This is partly due to the fact that, by design, Windows 95/98 has a limited ability to allocate system resources (like memory), no matter how much RAM memory is in your PC. In other words, even if you have 256MB of RAM memory, it is possible forWindows 95/98 to "run out of memory" if you have many applications running at the same time. What is the solution? You could upgrade to the significantly more stable, significantly more complicated, significantly more expensive Windows 2000 corporate operating system, which has an unlimited ability to allocate system resources. Unfortunately, because compatibility with older hardware and software was not an important consideration when Windows 2000 was designed, it may not recognize your PC's older sound card, modem, scanner, network card, or other devices. All things considered, you might be better off living with the problems for now and waiting for Microsoft to develop a more stable operating system for home use.
Your PC's hard drive is sort of like a small sealed record player, with spinning metal records and several magnetic "needles," that move in and out, reading and writing information onto the records. Because a hard drive is both mechanical and electronic, it is more prone to wear and to errors than purely electronic devices, like your PC's RAM memory chips. Because hard drives have moving parts, it is normal for every hard drive to develop small bad areas that are incapable of reliably storing and retrieving data. That's why you should run the Windows ScanDisk program (found in Start/Programs/Accessories/System Tools/ScanDisk), every few weeks. ScanDisk looks for data errors on your PC's hard drive and tries to fix them. It also electronically finds and marks the bad areas of your PC's hard drive, so that they won't be used any more, sort of like putting orange plastic construction cones around them. If there is any data in those bad areas, ScanDisk moves that data to another area of the hard drive. The problem is, if you don't run ScanDisk every few weeks, or if an area of the hard drive has gotten so bad that ScanDisk is unable to correctly read some data that it is trying to move out of that area, you could end up with corrupt data or programs, and that could cause your PC to lock-up. If ScanDisk is unable to move some data from a bad area of the hard drive, you may have to manually save your important data onto floppy disks or some other form of storage, format your PC's hard drive, reinstall Windows 95/98 (which runs ScanDisk first, to mark the bad areas), and then reinstall all of your software and restore your important data.
A year ago, the college where I teach bought all new computers for one of my classrooms. For over a month, every time I taught in that classroom, 4 or more students would complain that their PCs had locked up, usually a half-hour or more into the class time. After numerous complaints, our tech support people finally discovered that the non-standard mice that had come with the new computers had their own special mouse driver software, which had to be installed on each PC in order for the mice to work correctly. If you used the standard mouse driver software that is included with Windows 98, each PC's mouse would work for awhile and then cause the PC the lock-up. At the mouse manufacturer's Web site, one of our tech support people downloaded the newest mouse driver software for those non-standard mice, then installed it on each of the new PCs, and the lock-up problem immediately went away.
If either your mouse or keyboard connector is partially unplugged from your PC, it could be intermittently disconnecting, causing your PC to lock-up. Make sure that both the mouse and keyboard connectors are securely plugged in all the way. Also, make sure that your PC's mouse and keyboard aren't plugged into each other's ports on your PC. Because the connectors themselves look exactly the same, most PCs have some sort of icons or label, indicating which is the mouse port and which is the keyboard port. Unfortunately, because those ports are usually on the back of the PC, where it is hard to see them, it is easy to accidentally reverse them, which can cause your PC to randomly lock-up.
Along with a hard drive, which provides long-term storage of software and data when your PC is turned off, every PC has a some RAM (short-term electronic chip memory) installed in it, to hold the software and data that you are using at any particular time. When you start a software program, it loads from the hard drive into the RAM memory, where the PC's CPU (main brain) can access it. Because it has to be running all the time, Windows loads first, and always takes up a certain amount of your PC's RAM memory whenever your PC is turned on. As the Windows Desktop (icons and background) appears, some other software applications (anti-virus software, scanner software, and others) may start automatically, with each one using some RAM memory. You can usually see tiny icons for those applications in the System Tray, next to the Windows clock in the bottom-right corner of the screen. Some PCs have only a few of these StartUp applications, while others have 10-20 running all the time, with each one using your PC's valuable RAM memory. In addition, each software application that you run (word processor, email, etc.) takes up even more RAM memory. If your PC has only a small amount of RAM memory, and you try to open a large sound file, a digitized image, or anything else that takes up a lot of memory, it is possible to run out of memory, and when Windows runs out of memory, it locks-up. How can you tell if your lock-ups are caused by running out of memory or not? If your Windows 95/98 PC has 24MB or less of RAM memory, then Windows is using most of your PCs memory before you even start running your word processor or other application, so pretty much anything that you run could take up enough additional RAM memory to make your PC lock-up. If you sometimes run 2 or 3 things at the same time, or if you have many tiny icons in the System Tray next to the Windows clock, your PC should probably have at least 64MB or more of RAM memory. If you sometimes run more than 3 things at the same time, or if you're running memory intensive applications like image editing software, your PC should probably have 96 MB or more of RAM memory. If you run an Internet browser, email software, Web-creation software (like FrontPage) and graphics software, all at the same time, then your PC probably needs at least 128 MB of memory. How do I know that? Because my PC has 96MB of memory, and it sometimes locks up when I run all of those things at the same time. What can you do to trim your PC's need for RAM? If you know what you're doing, you can delete the icons of unnecessary programs from the Start/Programs/StartUp folder in order to prevent them from automatically starting up each time you turn on your PC. Because you're only deleting each program's shortcut icon, the programs themselves will still be on your PC's hard drive, and they should still show up in the Start/Programs, so you'll still be able to start them manually if you ever need them. If you don't really know what you're doing, you'll be better off leaving all of the icons in the StartUp folder, rather than taking a chance of deleting something important. If you'd like to monitor and control how much RAM each of your applications is using, as well as optimize your PC's memory cache, you can find a link to download Memory Plus (free 30 day trial, then $19.95) on my Software page.
As described in the section above, Windows 95/98 and each application that you run takes up RAM memory and other resources. As you close each application, it is supposed to free up the resources that it had been using, to allow other applications to use them. Unfortunately, this doesn't always happen. A complex application may use hundreds, or even thousands of resources, and unless it was extremely well written by its programmers, it may forget to give back many of those resources, or it may even intentionally keep some of those resources in anticipation of them being reused. This is known as a "resource leak." As you run and then quit several different applications, your PC may have less and less resources available for use by other applications, due to resource leaks. What is the solution? The simplest one is to restart your PC after you run many different applications. That will clear all of your PC's resources for use by other applications. If you want to learn more about resource leaks, read WinMag.com's article, Resource Leaks, by Fred Langa. Update, March 31, 2001: WinMag.com has gone out of business. Check Fred's Site to see if they have allowed him to publish that article himself.
While most commercial software is written in such a way that it gets along with other software, some poorly-written software "doesn't play well with others." Software conflict problems sometimes occur randomly, and are extremely difficult to diagnose, unless the lock-up problem appears right after you install a new piece of software, and it disappears as soon as you uninstall that piece of software. To give yourself a fighting chance to figure out software conflicts, never install more than one piece of software at a time on your properly-functioning PC. Each time you install a piece of software, use the PC for several days afterward, without installing anything else, to make sure that the new software doesn't cause any problems. That way, if a problem starts a few days after you install something, you can uninstall it and see if the problem goes away. If your PC has hundreds of little programs that you downloaded for free from all over the Internet, and you have no idea which one might be causing your PC to lock-up, try keeping a record of what you were doing each time your PC locks up. If you can't see any pattern to the lock-ups, you may have to manually save your important data onto floppy disks or some other form of storage, format your PC's hard drive, then reinstall Windows 95/98 and only a few of your most important software applications. Use the PC for a few days, and if there are no problems, start adding other software applications, one at at time, using the PC for a few days before adding each new application, until the problem reappears. Then, uninstall the last thing that you installed and see if the problem goes away.
Hundreds of new computer viruses are created each year. Modern computer viruses can do all kinds of damage. They can email your AOL username and password to someone in another country. They can destroy the operating system (Windows 95/98), the software applications (Word, Excel, Outlook), and the data files (taxes_1999) on your PC. They can email themselves to everyone in your email address book, making it look as though the email message is from you. They can also corrupt your software or your data files, causing them to lock-up your PC. The best way to protect your PC from computer viruses is to install professional-quality antivirus software, and to update that software at least once a month, usually by connecting to the Internet and using the antivirus software's automatic update process. The 2 leading commercial antivirus software packages on the market today are McAfee Antivirus from McAfee, and Norton Antivirus from Symantec. Having tried several antivirus solutions, I use AVG Antivirus, which is free, and which you can find a link to download on my Software page.
I listed this one last, because it is a real long shot. RAM memory is extremely stable and very rarely ever goes bad. However, it can be damaged by static electricity, like if your house is really dry in the Winter, and you walk across a carpet and then touch your PC's keyboard, giving it a static "zap." If any part of your PC's RAM memory has gone bad, then every time your PC tries to read or write data to that part of the memory, the data comes back corrupted, and that can cause your PC to lock-up. If there is a bad section of RAM memory, but it is way "at the end" of the RAM memory, then your PC may not even have to use that part of RAM when you're doing your normal PC tasks that don't use much memory. In fact, if your PC has bad memory "at the end" of its RAM, it may only have to use that bad memory when you're running a lot of memory-intensive things at the same time, and that situation could easily fool you into thinking that the lock-up was caused by running out of memory or by a software conflict. If you'd like to test your PC's RAM, you can download and run software like DocMemory RAM Diagnostic Software which may or may not still be free by the time you read this, but you can find a link to it on my Software page. Like other RAM testing software, it works by repeatedly writing and reading data to the RAM, to make sure that every bit and byte reads correctly every time. Usually, you start memory testing software and leave it running overnight, then check it in the morning to see if your computer's RAM has passed every test or not.
I was reminded of this long shot by Mark Guy. It is a long shot is because it probably only applies to people whose PC lock-up problems started only after they added one or more internal hardware devices to their PC, like a modem, an additional COM port, a video card, or a sound card. An IRQ (interrupt request channel) is a hardware signaling method that allows each hardware device to send a signal to the PC's motherboard on a unique channel whenever it has a request that needs attention, like a student raising their hand in class to get a teacher's attention. Each hardware device in a PC is assigned an IRQ when it is installed, sometimes by a switch or other hardware setting on the device itself, and sometimes by the Windows operating system. When you buy a new PC, its devices should already be set to their correct IRQ settings by the PC's manufacturer, so it shouldn't have any IRQ conflicts. However, if you add a new internal device to your PC, you could experience IRQ conflicts that can cause your PC to lock up if the new device has an IRQ setting switch that is set incorrectly or if the "Plug and Play" feature built into Windows incorrectly assigns the new device to the same IRQ as another device (a problem that happens often enough that many of us refer to that feature as "Plug and Pray.") When two devices are configured to incorrectly share the same IRQ channel, the PC intermittently locks up because it receives an interrupt signal on the shared IRQ channel, it can't tell which device is trying to get its attention. One way to avoid IRQ conflicts is to read and carefully follow all of the installation instructions whenever you install any new device inside your PC. Another way is to remove any device that you don't need in your PC, to free up its IRQ for a different device to use. For more information on IRQ conflicts see ZDNet's article, What Can I Do About IRQ Conflicts?.
PC lock-ups can be caused by a lot of different things. If your PC is
locking up, you will have to use some knowledge, some logic, some trial-and-error,
and some detective work to solve the problem. I hope that this article
has given you some clues to make that process a little easier.