Those dreaded and accusatory messages -- illegal operation, invalid page fault, general protection fault -- often are the computer's way of telling you, among other things, that it is experiencing serious memory problems, even if you have 64, 96 or 128 megabytes of RAM. Windows and the programs that run under Windows use up a lot of that memory.

As you open and close programs during the day, more memory gets soaked up. And as you travel the Internet, opening graphic-laden Web sites and downloading information even more memory gets eaten up.

Windows knows that you are likely to need a lot of information, so in order to give itself -- and you -- some maneuvering room, Windows, as it starts up, lays claim to a sizable part of your hard drive's free space and creates a special file known as the swap file. The file is also known as virtual memory. As the computing process lopes along, Windows transfers stuff it does not immediately need out of RAM and into the swap file. When it needs the transferred material it calls it back into RAM and moves something else on to the hard drive. The process continues until you shut down the computer and the swap file is erased. One simple solution is to reboot to clear out all the debris that has accumulated in memory. X The invalid page fault message (and other similar messages) may be telling you that the swap file is having a nervous breakdown. That can happen if your hard drive is so crowded that Windows cannot find enough room to create a swap file large enough to suit its needs or if one of the applications you are using has clobbered the swap file. The best thing you can do to help Windows create a stable swap file is to clean out your hard drive by uninstalling programs and deleting files you no longer need. Clean out the Temporary Internet Files folder, if you are using Internet Explorer and the cache folder, if you are using Netscape.

Clean out your TEMP folder as well.

And once you are done deleting these, be sure to empty the Recycle Bin. At the end of it all at least 10 percent of your hard drive should be free

-- and remain so at all times.

Then, defragment the hard drive. The utility for doing so is found at Start/Programs/Accessories/System Tools and is named Disk Defragmenter. Don't be surprised if Degfragmenter asks you to first run ScanDisk because there are errors on the drive. Do so, then run Defrag again. And, since memory is so cheap these days, you should also consider installing enough additional memory to give your system 64 megs or more of RAM, especially if you d a lot of fooling around with audio and graphics files.

If you have enough memory already, you have enough free space and your drive is defragmented, simply reboot after getting the error message. It is a good idea, by the way, to clean out your TEMP and Temporary Internet Files folders on a daily basis. If despite your best efforts you are still confronted by the invalid page fault message, it may be that, in addition to the program that seems to be triggering the message, you have another program running that is also trying to change file on which you are working. There is in other words, a conflict between the program you are trying to run and some other one in memory.

Should that be the case, you will need to close the second program while you are using the program that seems to be acting up. X There are as many explanations for the illegal operation message as there are programs. But there are a few common causes: One of the program's components may have been damaged. Uninstall, then reinstall the program. The program may be at war with another program. Using the System Configuration Utility in Windows 98 or Windows Millennium Edition, set up Windows to run the troublesome program plus only one other program at a time until you have found the program causing the conflict. Then either uninstall the second program or stop it from running when the program that is crashing is in use. You have an out-of-date or corrupted driver for one of your devices. Reinstall your drivers or, better yet, update them. An overabundance of files in your Temp folder can cause all sorts of weird problems, including illegal operations. Clean it out. Unknown file errors may be causing the illegal operation message. Check your hard drive with ScanDisk. Also, it would not be a bad idea to ensure that 10 percent of the drive is free, and that the drive is defragmented. If none of these suggestions helps and the problem recurs, contact the program's vendor. The program may be marred by its very own bug. X

Memory problems, a dysfunctional swap file or two programs grabbing for the same information can also trigger that other ever-unpopular Windows favorite, the General Protection Fault message.

GPFs, though, can also crop up if your computer is not using the right device drivers or if some of the files that make up Windows have been deleted or corrupted.