1) Clean your computer, get a can of compressed air, make sure all heat sinks are free from dust, make sure all areas of your machine are free from dust.

2) Increase the airflow into your machine, have a fan at the front to suck air in, and one at the back to blow the hot air out.

3) Failing those options consider replacing your graphics card fan with a monster fan, artic cooling do a load for nVidia and ATI.

Thank you come again