So the other day I was getting around 100 fps on low with the GTX 670 now all of the sudden I'm getting about 40-50. This is really weird and I don't know whats wrong with it. Any help would be amazing

PC Specs:

Intel Core i5 2500k
Gigabyte GTX 670 Windforce
8GB Corsair Vengeance
MSI P67A-GD55(B3)