Trojan Gen 2 Trojan Zero Access Need help removing

I seem to have contracted both the Trojan Gen 2 and Trojan zero access viruses.  I have tried to remove them using Norton Power Erasor and Fix zero access with no success.  After each scan, I am being told that I have to remove the viruses manually.  I am not sure how to do this without any help.  I am running Windows 7 64 bit and I have a flash drive.