From: Midwest, USA
I had a similar problem. The pc would run fine and then start rebooting itself. Then it would run fine for days and then start rebooting. I swapped power supplies, hard drives, video cards, etc. I had two memory dimm's and swapped them and the problem was solid. I then removed them one at a time and found that one of them was "bad". Replaced both of them and have not had spontaneous reboots for 2 years now! Sounds like you have a hardware issue.