I have a similar problem now, and i think its a little bit different.
When I cold start the computer, it starts restarting randomly, with breaks of 0.5 seconds to 3 seconds, sometimes it restarts, and when I see the first BIOS screen, it restarts again and restart again within half a second. Sometimes it went upto windows startup log, or scandisk screen and then again restarts.
BUT the most important thing I want to mentioned is that the frequency of restarting decreases as time goes. After about 6-8 minutes the computer becomes stable and then I can run at for several hours or even 2 days without any problem.
All this happens when I cold start it. When it becomes stable, I can restart, reboot, eand do anything without any problem.
I have checked the PC with: Norton Antivirus, F-Prot (All updated) and nod32 DOS. All erport it clean.
Checked with Ad Aware, no problem reported.
Another thing I think must have to ention here, that I had to temporarily shift my PC to the basement for 3 days, there I used it, when I shifted back to my room, the next day brought this problem. Then I noticed some sort of movement/noise in my PC and openeed it and lolz it was a little mouse (animal not my hardware mouse) inside my PC, Transported that mouse to highway (I threw it with maximum velocity). I chcked the internals of my PC all seems to OK. The first thought that came in my mind was that the mouse might have been destroyed some wirings, but I checked all OK.
Though I dont think the mice was the cause of this problem but I mentioned here as I need to come to a conclusion analyzing every aspect lolz.
Sorry my post is so lenghty. Any help ? any idea? OR i m gonna become a rat killer machine?