Low fps after re-installed windows 7

I recently re-installed windows 7 home premium 64-bit and I'm not getting as high fps as before, for example in League of legends I had capped graphics setting and got a constant 60 fps, now I'm staying around 40 fps and dropping below 30 at times.

My computer seems to preform worse then before I re-installed windows. I can't seem to figure out if it's the GPU or the CPU or something else that I've missed.

Would love some feedback!