Hi,
the PSU is new EVGA SuperNOVA 850 G2. I tried to isolate the riser but they all working when 3 GPUs are connected. I tried connecting GPUs one by one (starting from slot pciex16_1) and windows detects and installs drivers without problem. But when I connect 4th card into pciex1_3 slot, windows boots up not showing that GPU(fan is spinning like on other 3).
Thanks.