driver slowdown

playing my game, the app froze for ~2secs when it restarted moving one of the textures looked like a checker image.
so i exit the program + restart but rendering performance is like 4x slower (no checkered textures though), shut down most background apps + retest but still the same.
logging out didnt help
performance only returned to normal when i rebooted the computer

this has only happened to me once but i seem to recall ive read about other ppl experiencing something similar + so wanna nip it in the bud ASAP

cheers zed
btw geforce 7600 GS

Something like that happened to me when I killed the driver by forgetting to deallocate my textures and do other cleanup when my program terminated. But that was like 4-5 years ago.