I have in the distant past found AVG AV a bit lacking when it comes to trojans, or at least the one that got my computer.
Trojans generally require something with a better detection/clean engine, that knows based on the detection where the important nooks and crannies are that the beast is likely to hide to re-spawn its nasty self.
Prior to whizzing over to a forum where they do HJT analysis/disinfection, you may wish to try
Superantispyware (which I've read mainly very good reports about) and/or
Asquared I'd run both, in turn, and then repeat in safe, and if nothing further is found, delete all the system restore points (where it is also likely to hide) then hopefully you're good to go.
If you have bank/CC passwords or important data, OR the above doesn't appear to fix it, it would definitely pay to go to a specialist forum. Or reformat/reinstall.