If I recall correctly, I've only seen this in Win95 machines but I really suspect power issues.
A machine could be in use or it could be idle - out of the blue it reboots. This phenomena is very intermittent. I've searched high and low for info. on this - including MSKB - and have only found info. specific to non-MS OSs (nothing @ MSKB).
The most recent machine I've been told this is occurring on is running Win95 - they are also experiencing parity errors. They swapped out the RAM - and the problems remain. The machine was fine in my shop but when installed on-site - w/in a couple of days they started experiencing these problems. I'm suspicious of their office wiring. I'll have the system back in my shop this week. If the system passes ok in-shop, I'll take it back to the site w/ a UPS in tow. I could be barking up the wrong tree. Any other advice as to how to nail this down would be greatly appreciated.