Sudden drop in gaming performance (FPS) on a mid-2010 iMac About two weeks ago, I had a sudden drop in gaming performance on my 27" iMac with ATI Radeon HD 5750 graphics. While before I could play games without any problems at high graphical settings, suddenly playing Diablo3 for example became unbearable with around 10FPS at the lowest possible settings. Oddly enough I simultaneously started having similar problems when playing games on my Windows Bootcamp installation on the same machine.

I am not noticing any other problems besides those when gaming. Rebooting the machine does not help at all.

What could be the problem and how can I solve this?
I had this and fixed it!

Basically something was overheating.  It would freeze as it hit the overheat temperature and then resolve once the temperature dropped about 5 degrees celsius.

So I downloaded some random fan speed app (link below), cranked it up to full speed and haven't had a problem since!

http://www.eidac.de/