Lately i cant open firefox or orkut,probably a virus,scanning did not help?any suggestions?

when i open firefox the dialog box appears "I dont hate FF use IE instead you dope" n closes the window, n in IE when i try to enter orkut it says "This program is banned,not by the administrator but guess whom?? muhahaha" not to forget the sinister laugh tht accompanies tht...........n the window closes. cmon guys n gals nebody who could help???its been days since i accessed my orkut.....who oh who will help this poor soul??