System freezing during video

Hi,
My system has been freezing recently. It usually happens when watching video and more often when watching streaming video than playing a video off my hdd. When it happens the system locks up and the audio goes into a repeating loop. Sometimes the hard drive light stays lit. Sometimes the system will recover on its own but I usually have to hit the reset button. No BSOD and nothing useful in the logs. All drivers are up to date.

I'm having a hard time determing which piece of hardware is at fault... The video card is most obvious because it happens while watching video but I'm not so sure thats the problem. All of my temps are in normal ranges during the freeze, I let memtest make a pass and had no errors (perhaps i need to let it make a few more passes?), and I just replaced the PSU although I had the same problem with the old PSU.

Please help!

Specs:
MOBO: XFX 780i SLI
CPU: Intel Q6700@2.66ghz Quad
GPU: EVGA 460 GTX
RAM: Corsair DDR2-800 6GB
HDD: RAID 1 with 2x WD 500GB and 2x WD 1TB
PSU: Corsair HX750
OS: Windows 7