Thanks for the advice. The system does not lock up. It just gets the blue screen and reboots. After reboot, some BIOS settings have changed (to their defaults?) and an NTDETECT error occurs. I have to reinstall Windows 2000 to use the system. This is why I put the OS on a separate partition.

It doesn't require a lot of CPU usage to crash anymore. Just using Powerpoint for a while kills it. Also, I checked that the fan still runs. Apparently, the BIOS does not have temperature printouts.

The system is vintage 2000. Maybe the motherboard has gone bad? Would replacing it be worthwhile (cheap)? I'm also interested in replacing the CD-RW drive since the front panel has become detached (although it's still useable).