Well, many of these Trojans remain hidden somewhere on your PC, even if it seems that the problem has been Fixed. The First thing you need to do is to Work in Safe Mood, and doing a couple of Steps such as turning off system restore & also Hidden Files....
it is Crucial that you work offline when cleaning up your PC. Current Trojans that hijack your PC can not get removed when your doing a clean up online....
When that's done, then u need to run 3 or 4 good programs ( 1 anti Virus, 1 spyware, 1 Adware & another one that mixes all )
Every Virus or Trojan is created differently, so some Programs might work & others might not....
What is your current Anti Virus program?
The best tool that I have and use is a program called " Hijackthis ".. it is only recommended for Advanced users but it is such a Powerful Program because it scans all your PC's and tells you Exactly what you have Got & what you havn't....I Strongly recommend you Downloading it.. its Free