googled - Mac Antivirus
I see Avast! Mac edition on there. Avast is what I use on all my windows machines with good results.
norton makes an antivirus for macs now
If I were you I would make an appointment with the folks in your local Apple store Genius bar. The Genius Bar is created to diagnose and fix problem with Apple computers. Simply make an appointment, bring your computer up there and if it's an easy fix they'll do it right there, but if it's more difficult they will keep your computer for a day and you can pick it up the next day with it running good as new. :)