It might not be a virus - it could just be bad or corrupt software or even an obscure hardware fault - might be a virus though.
Best to buy and install a proprietary Virus checker programme - free ones also available & if you Buy Norton Security (Firewall & Virus protection) in the UK you'll pay Irish VAT at 21% !!!
You might wish perform a system rebuild if you have the disks and the key.
Other free S/W that might help you is Piriform's CCleaner and Spybot Search & Destroy
Never open an attachment to an e-mail unless you're absolutely certain that you can trust the sender - even then the sender might have been duped into sending you a naughty file without their knowledge.
It's a minefield out there...
Peccavi
September 2009