Graphic crad overheated and the fan does not run.

My toshiba satellite A505-s6986 laptop graphic card got overheated. This happens when I play a video file or play a game. The laptop boots up normally with the fan spinning but after that the fan stop working. It sometimes works; however, the system freezes and the mouse and keyboard stop reponding. You can feel the heat at the bottom of the laptop.
The pocedures I have done:
1. I cleaned the fan and heat sink
2. I updated the bios
3. I changed the RAMs and the hard drive

***The result is the same

P.S I use Windows 7 *64 and the laptop has got two graphic cards, free and built in.

Any solutions?