Do I have a virus?

This is my secondary computer and as such is a cheap one. Not sure what kind of motherboard, and it has 2 GHz processor, 256 RAM Memory.
OS is Windows XP. My mother has been using it and she said she opened a suspicious attachent which did not have anything in it. Since this happened (four days ago) everytime the computer is turned on as it is going through booting it stops on the back screen and it tells me to either press F1 to enter setup, or F2 to go on with the default settings. I tried tried F! and changed the BIOS but after that I could not turned it on so I had to reset the CMOS. If I go with F2 it loads XP and it seems like things work ok except that the screen has gonne completly blank "out of the blue" at least four times. Could all this be happending because of a virus? If so what do I need to do? (I currently do not have any antivirus software installed)

 

Does it let you enter windows? SOUNDS LIKE THE EXACT SAME THING HAPPENED TO ME. Someone fixed it though.

 

Yeah, I can enter windows and use the computer, sometimes for quite some time before the screen goes blank. Also, after this happens if I wait for a while it I can turn it on again (of course I have to do F2).

 

Have you run a virus scanner on your machine?

 

No, not sure which one to use.... Any recommendations???

 

http://www.majorgeeks.com/download.php?det=1968

there ya go