I run AVG in my wife's windoze box. It can detect (sometimes) a trojan, but isn't likely to kill it stone dead.
Not that I like doing it, but with no other programs running, run AVG, then pull the plug out of the socket. Trojans often can sit in memory and then imbed in any file at random. Having cleaned infected files, still leaves the beasty sitting in memory til it reacts to power down cycle. How it does that I don't know, but after cleaning a variety of files only to have a new one infected on next boot up, I have found the brute force method very decisive.
I believe that was the reason MS introduced the Ctrl+Alt+Del. login requirement with windoze NT, this keying sequence killed any trojans waiting to infect......or so I was told and that is where I got the idea about trojans sitting in memory from.
I should add that the above method will not get rid of a non trojan virus, and I offered the above based on the thread heading.
But by far the best possible solution is to give windoze the flick and start running a Linux distro ...ubuntu, Linux mint etc.