Check out Rkill, TDSS Killer and Combofix. 9 times out of 10, Those tools will find and clean up a trojan/rootkit. You should get them all at bleepingcomputer.com to avoid fake versions.
Run them in that order too. You'll have many options for Rkill. Rkill.scr is what consistently works for me. It's disguised as a screensaver file so most malware wont notice/block it. It will search for any known processes and kill them for the current session (until you reboot).
TDSS Killer is a rootkit scanner. It has saved me a number of times, but often it doesn't pick anything up at all.
Combofix is by far the best tool I've ever used. It may need Admin access to run though. If you don't have it already, it will probably want to install Microsoft Recovery console. If you cant install it because of lack of admin rights, you could skip it, but there's potential for it to screw up an operating system file and you would not be able to recover it.
That said, I've probably used it near 100 times and I've never needed the recovery console.
I just have microsoft security essentials (free) and keep it up to date and a full scan every now and then and no problems.
What works best changes pretty frequently, but I've found security essentials to be useless lately. I was using and recommending it last year, but most of the malware around now will just kill it.
As far as anti-virus goes, I'm currently using the free version of Avast. It works very well. Fully automated updates and scans, and I love the "silent/gaming" mode. It never pops up for any reason.
For malware, I use the tools above. Malwarebytes used to work well, but most malware now will destroy it, literally. Even after the malware is gone, it wont work and uninstall and reinstalling wont work either. I've figured out how to fix it before, but I don't think it's worth it.
At work my boss and I have found that the only mainstream software that work consistently are paid versions of Stopzilla and Spyhunter. Both have more than their fair share of downsides (slowing any PC they're on to a crawl, Disabling legit software without notifying you etc.), but when it counts, they work.
Whew, long post, I need a nap now.
