Isolate it by excluding other GPU's, like installing 1 GPU 1st fire up claymore if success, then 2,3,4 by then you could determine what might be the problem, most common will be the Riser and your PSU, ensure that your PSU could handle 4 GPU power.
I will try this when I get home. The PSU is 1200W Platinum rated so I think it should be good.