I suggest that you completele format and reinstall your system. Theres lots of ways to clean up a windows, but it dosent worth it, there cant possibly be an anvivirus/malvare/spyware what could kill all the enemy files in a system.
So what I suggest is that you set your system again, and you'll get your "very fast" PC back, which I doubt its fast, since 40-50 fps is damn slow.