It would be worth trying removing the processor and carefully blowing out any dust in the LGA775 socket (I assume that's what it is if it's a corer2 duo). I made up a new games box a while ago based on the shuttle SX38P2 unit, with a core2 duo E8400 processor in it, and had remarkably similar symptoms. It would run happily for some time, then just die on me. Other times, it would just reboot over and over. All this was during windows Xp installation and was very frustrating.

Having reseated everything several times, I ended up swapping almost every component from my CAD box into the shuttle, and vice versa. Everything ran perfectly on BOTH systems! I installed windows, then swapped the parts back. It STILL ran perfectly.

Before I put the new processor into the shuttle for the last time, I checked under the microscope and found a couple of fine hairs in the socket, which I removed with tweezers. I'm assuming that this may well have been the problem all along. Possibly one or more of the spring pins in the socket had been making intermittant contact, and the last-but-one processor swap finally dislodged it. I don't know for sure, but the thing has been rock-solidly stable since, even overclocked from 3 to 3.6GHz.

It's also easily the fastest computer I've ever owned. Probably as fast as all my other computers put together

So check your CPU.

pca