Sounds like a hardware issue to me.
If your confident, take your PC memory sticks out and the cards (graphics, network, sound cards etc) and put them back in again as securely as you can (1 at a time, graphics card and 1 memory stick first, then see where that get's you). Always listening for the 2 clicks when inserting memory, and switch the power off at the socket, but leave it plugged in - it's best to earth your PC when handling small components.
I had a similar problem with Windows2000, turned out to be some cheap memory that had become deadly sensitive to heat, once I swapped it out everything was peaches again.
Nunuman,
Just approved your post so I could tell you that we won't approve posts with a single unhelpful and pointless word in them. It's more trouble for us to approve posts than simply leave them hanging, so make it worth our while please.
Van-B
It's c**p being the only coder in the village.