Windows 7: Computer suddenly slow after playing Assassin's Creed 2

My computer has become awfully slow after playing Assassin's Creed 2, I was playing then my audio went fuzzy and the fps went down to like 2-3 fps. It has been slow ever since, all my graphics card options reset so I fixed them then tried a registry cleaner.. It worked to some extent but my games are still laggy. I need some suggestions, and my hard drive is clean and I have 4gb of RAM plus an i5, my GPU is a Nvidia GT 540m.

~64kGamer

Try running task manager (and resource monitor) to see if anything is suddenly hogging CPU. Another free tool is Process Monitor. It gives a deeper look at what's happening with your machine. You could also try scanning with Malwarebytes Free. It picks up things that other traditional antivirus suites miss. Update the signatures and run a full scan. If these don't help you could try a System Restore to a date/time prior to when the issue first began. If no restore points are availabe you could also make sure your temp files aren't overflowing and you clean out your browser cache.