Unexplained Lagging/Low FPS (Please help!)

[CodeinePoptart]

Now before there's someone who claims it's a requirements issue, I'd like to mention that I've played 9 hours of this game on max settings and high resolution with not even the slightest drop in frame rate.

When playing the game, my memory is at around 20% and my CPU is at 3% and the graphics card does just fine as well.

I did not start lagging until I re-installed Windows 7(Ultimate, 64-bit).
Could someone please help a bit?

The Symptom: As soon as I reach the menu, the frame rate is incredibly low and there is mouse lag due to this. I can load games just fine but it is incredibly choppy. The audio seems to handle just fine.

Here's what I've done so far:
-Verified Cache
-Put settings on Min

[Bees]

Use GPU-Z to make sure that your video card is raising from idle to full clock speeds when you're in the game.