You would need to contact EA but you should read this thread and post about video cards that overheat. I Know you don't have Nvidia but same rules would apply.
http://forum.thesims3.com/jforum/posts/list/693844.page
The sims 3 does not have a frames per second limiter. So you have to go into your Nvidia control panel and enable Vsync . It will lock the frame rate at 60 and stop the card from overheating. Otherwise the game will push the card continually to its max frame rate and overheat it.
You can also monitor your FPS in game using a cheat. Control+Shift+C, testingcheatsenabled true ( enter) fps on (enter.) Your fps will show up on the upper right hand corner of the game
