Does it happen while gaming or on desktop ? What is the make and model of the card you are complaining about ? Other system specs: PSU, motherboard, etc.
Have you done a memory check with http://www.memtest.org/
? Create a bootable CD and boot to it. Run the test for as long as you can, preferably overnight.
Update all your drivers. People having Realtek sound boards say the problem is due to Realtek drivers making gfx drivers crash.