Pc restarts...

That could be a lot of different things. Need more information.

Does it restart every x time frame? Or is it you're running something and it goes? Does it do a windows shut down and restart or does it just shut down and restart?

More information will allow for a better diagnoses.

What OS are you running? If you are running the Win 7 Release Candidate, then it started rebooting your comp every 2 hours because its expiring.

Are you getting a BSOD?

Yeah,i m runnin win7...
N also,it just restarts,nt on a particular activity...

are you running the release candidate of win 7 (build 7100) or are you running a retail version of win 7? Also- have you monitored your temps at all on your CPU or GPU or anything like that? sometime overheating can cause your comp to reboot.

Yes,m runnin win7 rc 7100.....i havnt monitord ny temps...hw cn i do dat

If you are running Win7 rc build 7100- it is time to install an official retail version because the RC is now expiring. It will shut itself down every 2 hours, and there is nothing you can do to avoid that. Its time to install a real OS.
Edit: here is a link for ya
http://www.tomshardware.com/news/windows-7-rc-restarts-...