FPS Rise and Fall

So basically here's my problem. The frames per second in the game for me run at about 70 +/- 10. Lately there has been the problem of it jumping up to 200, and then falling to 0.7. its a problem worse then ping lag. I have a clean system, no viruses, and running norton internet security. It does not like crossfire, so i have isolated it from it's scans, thus removing that problem. All non-essential programs are shut down, yet i am still having this problem.


Does anyone have any idea how to fix this to have a stable and reliable frames per second, which does not fluxuate from ranges of 200 to 0?