I want to know that if there is a virus in a computer then how to find it and delete it ?

Virus is not detected by antivirus or antispyware, my computer sceen is blinking sometimes 3times/30second and sometime no blinks. I formatted C drive but problems comes after 10 or 12 days again, I know that if I format the whole hard disk then this may be solved but I want any other solution. My pc has intel g33/g31 graphic chipset family and dual core processor 2.8 ghz .

You many know or not know that your PC is infected with Virus or Trojans. It depends upon the usuage of your computer. If you are using the PC daily and working on same application you can easily come to know whether infected with virus or trojans.

As you already formatted C drive, so after 10 or 12 days again the same thing happens which means virus or it's traces are still in other drivers you need to clean those infected drives. You are using antivirus in this case if you are using trial software or free licensed version it works for with limited features only. If you still scan with that it detects threats on the basis of virus definitions. Make sure to check the reviews of the antivirus before downloading.

Install a Internet security instead of antivirus if you are connected to internet becuase internet security software is loaded with great features that detects the traces of virus or trojans, It prevents automatically downloading of other malicious softwares, toolbars...etc