Trojan Virus Removal

I have a Dell Inspron 620 approx 13 months old, running McAfee anti virus software.

I have 2 trojan viruses which are causing problems, one of which is to continually disable the firewall.

McAfee is detecting them but is unable to delete them.

I would appreciate any suggestions on the best way forward to deal with them. I have looked on the net and one suggestion was to run a complete scan in safe mode, which I have done. This did not detect the viruses so did not achieve anything.

I was wondering if setting the computer back to factory setting, as it was shipped to me may be the answer, but am not sure if it will detect the trojans.

I am running Windows 7.

The viruses are identified as : RDN/Generic BackDoor!sl