FPS goes down when I move my mouse

Hi all, I've had ro2/rs for a while, and it has ran fine. I have not had any problems with it. One day I got to play the game, and when I move the mouse, the fps drops a lot :confused: . wsad is fine, but moving the mouse just causes the fps to go down, even though it wasn't doing this before. What should I do? Specs. 12 gb of ram, amd 7970, amd 8 core 3.1.1 GHz.