Tell us about your Power supply , with the NV GTA 560 , You need a min. PSU of 450 watt, and a 12 volt 24 watt power connected.
oh, if anything my power supply is overkill. it's a Corsair AX 850. I also tried an Antec TRUEPOWER Quattro 850 with identical results. both of the 6-pin PCI-E power plugs were connected to the GPU in both cases.