|is this ur power supply ?|
it appears it does not have SLI support, so probably its not giving enough juice for both 560's.
The next thing to consider is the temperature download gpu-z. Check ur temp at idle and when ur gaming,
I would like u to take out one of the 560's and let the pc run on one graphics card install the drivers for it and check if it happens again,
post back results
computers are a second home