About 6 months ago my computer began restarting unexpectedly minutes after startup. I thought this was a power supply problem and switched in my friend's supply. The problem abated for a few weeks but gradually came back even more severely - the computer would restart several times after every startup. At this point I decided to give my friend's supply back and buy my own (he claimed his gave him similar problems). I purchased a decent-looking model for 60$ or so, but after a couple of weeks the problem began again - once after every startup the computer will randomly restart. Under my previous two power supplies this was accompanied by a system beep but not anymore. So, my question is in two parts:

First, what could be causing this problem? And second, is there some type of logger that I can use to monitor when the computer restarts - one that ideally would give me some information as to which component is to blame?

Unexpected shutdowns are usually due to 2 possible causes: A bad power supply or CPU overheating. Since you tried 3 different supplies its unlikely that the PSU is causing this. So, you can monitor the CPU and case temperature using Everest Home. It also will tell you all sorts of information about your system.

If the CPU is overheating the mobo may be going into emergency shutdown to keep the CPU from frying. Check your BIOS for the shutdown temperature. Set it to 60C if you can. Prolonged high temperatures will shorten the life of CPU.

Are all the fans running ? Check the fans on the CPU, case, Northbridge and video card if they have them.

If the case temp is OK (35C or less) but the CPU is overheating then there are 2 possible reasons: 1) A bad thermal contact between the heatsink and the CPU; or 2) the heatsink/fan is inadequte for the CPU. I recommend removing the HSF, cleaning it with rubbing alcohol and a soft rag or tissue, and applying Arctic Silver 5 (a small amount spread with a credit card). If this doesn't bring the CPU temp down then you're in the market for a new HSF cooler.

I downloaded a system monitoring application and, bizarelly my CPU's average temperature seems to always hover around 60 C - all fans running. The temperature restriction on my motherboard doesn't even go down that low. It was set to 120 by default - I set it to 80, the lowest it could go, but the restart problem hasn't repeated itself since I've gotten the temperature monitor. The processor is an Athlon XP 2100+. What do you guys make of these numbers?