Abu Baker

Hi I have a problem with my gaming pc (intel core 2 duo,256 ati hd graphic card, 4 GB ram, OS: xp sp 2 and problem is whenever I start my game my lcd display turn off and after few second my computer restart. What is the I think It may be the Operating system or VGA problem but everything else work properly.reply me please my name is asus striker extreme plz reply soon as possible