SLI Help

I recently upgraded to a 2-way SLI setup and have been running into crashes lately. The PC will crash whenever i adjust graphic settings, or will crash in the middle of the gaming. I upgraded to the latest drivers and have had no better luck. Any suggestions?
  • AMD Athlon II X4 635
  • Gigabyte GA990FX-UD3 Rev.4
  • 8GB Ram
  • MSI GTX660 (2) SLI
  • Corsair TX750
 

Try each card individually. Make sure you're using the correct power cables.