PC turn Off in the middle of my movie marathon,syrfing in the net etc.

We need more information like computer model and others. Try doing a scan wit malware bytes. And also provide information about your problem. Like when this start to happen or does this problem occurs in safe mode...

System:Microsoft windows xp Professional version 2002
Computer:AMD Sempron(tm) Processor 3400+ 1.81 GHz, 448 MB of RAM Physical Address Extension

So what is your problem actually? How do you know it is a virus problem? We need to know what happen to your PC, that makes you think it is a virus?