I have a six month-old Celeron 333A with 64Mb of RAM and a two year-old 133MHz 686 with 32Mb of RAM. Both machines are operating with Windows 98, both share their hard disks via Windows 98 networking and the 686 shares the 333A's modem via SyGate 3.0 (I am thinking about upgrading to Windows 98 Second Edition for its integrated modem sharing).

This system worked fine for months until last week when the 686 began frequently to display the "Blue Screen of Death" (BSoD), which reports a "fatal exception", usually 0D or 0E at various addresses in VxD VMM(01) or VMM (06).

Sometimes this is followed by a "This program has performed an illegal function" error message window which sometimes also occurs without the BSoD. Sometimes the result is simply termination of the currently active program, but usually the machine ends up freezing completely regardless of any attempt to recover from the error.

The problem does not seem to be caused by any particular program -- I mainly use common programs like Eudora, IE5 and Word97 and it has occurred while using all of these, both when they are running alone and with other programs minimized.

The machine always restarts OK after the problem occurs, but it usually recurs soon after the machine is restarted. The problem usually seems to occur after the machine has been running for a while, leading me to suspect hardware more than software.

After researching possible causes and seeking advice from various people, I ran a virus check (no viruses were found), then re-formatted the hard disk and re-installed Windows 98, but the problem occurred during the re-installation process, strengthening my suspicion that the cause is more likely to be hardware than software. (I did eventually manage to re-install Windows 98 without interruption.)

I was advised to replace the machine's RAM (32Mb EDO), which I did, but the problem occurs whether I have the original RAM, the new RAM or both installed.

The problem does not occur on my other machine (apart from occasional and isolated occurrences, which seems to be "normal" for Windows).

Can anyone suggest anything further that I could do to diagnose and solve the problem, short of having the whole machine upgraded?