Trojan.Gen.2 removal

HI i just recently bought norton antivirus 2012 and its saying that i have the virus trojan.gen.2 and getting rid of it failed, so i tried all of their extra tools to get rid of it to no success and when i scanned my computer again it showed back up so what else can i do to get rid of this virus? Thank you very much for any and all help you can give me.