Grr. I tried upgrading the RAM on my computer last night. This should have been trivial, but my poor pc is now rather broken. :(
I got myself 2 512MB PC2100 DIMMs to replace the existing 2 256MB DIMMs. After a few failed attempts and a very sore thumb I finally get them installed. I switch on the machine. The BIOS finds the RAM and Windows XP boots correctly. Seems OK. To make sure I download memtest86 and burn it only a bootable CD. I boot with this and run the standard tests which take about an hour. These all pass so the RAM looks OK. I boot back into windows and go off to finish dinner.
I come back to find Windows has locked up. This is a very bad sign as prior to the upgrade the machine was pretty solid. Further investigation indicates that Windows now crashes about once every ten minutes. Also, in the process of checking for possible causes I find that my BIOS settings have been trashed. The part most likely to cause problems seems that it got reset to a non-plug and play OS. This may well have done horrible things to Windows' device configuration.
After setting the BIOS configuration to what I think it should be however, Windows still isn't stable. It's even crashed a few times during the boot sequence (once with the dreaded "IRQL not less than or equal" blue screen).
I've left it running memtest86 extended tests today to see if there are any hidden memory errors.
When I next get a chance to try to fix this I'm going to have to try the usual things of booting Windows in safe mode, swapping back in my old RAM and ripping out some of the huge number of PCI cards I have.
Any other bright ideas for tracking down this fault are welcome. The RAM BIOS settings are on autodetect which gives them the most conservative timings, so I don't think there is much I can do there.