amd athlon II x4 630 2.8ghz
nvidia gtx 560
yes i installed the most recent driver for it
not more than usual
hmm that sounds kind of weird, The fps usually drops when you run some resource consuming applications on your background.
The only advice I can give you now is-
Uninstall and then reinstall the gpu driver.
Then if the problem still exists, then try to roll back to the older driver.
p.s My gtx 580 is rendering 2-3 less fps after I installed the latest 300.42 drivers. Maybe your problem is somehow related to mine?