I wouldn't think so, those cables supply extra, but not (always) needed power to the CPU. Should be unrelated to this GPU specific problem.
What's the manufacture of that PSU? According to the specs given, I would assume it's capable, even without knowing the definitive wattage of the rails. I would still advise you to check temps with one of the above apps, to rule out overheating, and maybe even give us the clocks (rivatuner can do that) to make sure this isn't the work of an unstable OC.
If you can test with another PSU or even Graphics card, it might help to shed light on whatever's going on.