Graphic card shut down, what the ....

I was enjoying my new XBox 360 controller playing Mirror's Edge when suddenly my machine just shut down. It seemed like the graphic card shutted itself down because of overheat problem. So I went to ATI web site, find EAH4850/HTDI/512M entry, and downloaded SmartDoc535.zip and Version 9442.11.10.0.2.AS01 BIOS update. I hope they can solve my problem.