Game Freezing

I've began to experience moments where my game freezes my computer ever since August 16. I've never experienced this before (and I've been playing on this computer for almost 2 months now) and I've actually heard that its happening to my friend when he plays too.

I've also experienced a significant drop in frame rate. I used to get an average of about 200fps but ever since August 16, my frames averaged at about 60fps.

Any thoughts on what might be the problem?