more power than your PSU is putting out.
Try a more powerful PSU
Also, did you disable on-board video in ther BIOS?
I grabbed meself an old GeForce FX 5200 for free, and stuck it in my secondary computer which was on onboard graphics. Now, when i play any game or watch a DVD, no matter how graphic heavy, every so often, it will go very gittery, and almost freeze up for about 3-5 seconds, then it will go back to normal and everything is fine.
Any ideas would be much appreciated.