GTX 460 performance drop

Hey guys, recently (about 2 months ago) I finally got my new rig. It's an Intel Core i5-2500, and a GTX 460 1 GB. Until about a week ago, my system was fine. I have never been so happy before. I could max out basically every single game I tried. But my hapiness didn't last long enough. About 4 days ago, I installed some odd programs and applications here, and I started feeling a slight performance drop while playing Modern Warfare 3. However, I ignored it and continued playing. Ok, so I stayed until today without playing the heavier games, stuck on SA-MP. This morning, I finally decided to run Saints Row The Third, to kill some time. But when I ran the game, I got a terrible surprise: there was an unbearable lag. About 20 FPS. I ran to the Nvidia website and updated the video card drivers. Even though I AM NOT SURE IF THE GTX 460 IS THE PROBLEM. Ok, after updating the driver, I felt a slight improvement, but it wasn't so good as it was before, when my FPS was locked at 50. Ok, so I ignored it, and ran back to SA-MP. Then I decided to play Crysis 2 and finish the Campaign. I like shooting aliens in my free time. But after loading, I also felt a terrible lag on Crysis 2. My FPS was usually locked at 55-60, and suddenly, I wasn't getting not even 30 FPS, what the hell ? And now I am worried about my system, and I'm affraid it won't come back. Like I said before I AM NOT SURE IF IT IS THE VIDEO CARD. I also tried restoring my system, installing .NET Framework 4.0, installing DirectX 11, but nothing seems to work here ! HELP !