Games now laggy but shouldent be.= Answered

So most of my games have been laggy for a week now and they werent before. I did a virus scan, malware, almost everything I could find. Call of duty black ops was running fine then it went and stayed below 10 FPS, CoD Black Ops 2 lags and it didn't it stayed below 40.
This is a fairly new computer, it is an Alien ware with a Core I5, Nvidia geforece 650M, 6GB ram.

I could run these games on fair settings then it just got unplay able.

I dont have avg, and I run these games from steam.

Thanks