If it's giving you a 60 second countdown before restarting with a message that starts off with NT Authority... It's one of a couple of virus's (W32Sasser or the Blaster virus.
If that's not happening it could still be possible virus problems may may also be power supply of motherboard problems.
Hi, My computer has bein restarting without me telling it to. I don't know how to stop it or fix it. Can you help me. Thanks