Other possible causes:
1. Leaking capacitors on motherboard.
2. Overheating due to dust on CPU fan & heatsinks & power supply.
Scan with Ad-Aware, SpyBot & Stinger.
4. Are you running Kazaa, Imesh & P2P network?
I've have the same problem. I ask the same question at MS website and didn't receive any help. Does anyone have a solution? I've install a new hard drive, scan for virus, down loaded the latest updates and upgraded memory. I'm using a soney,
120g hard drive