Hi, I have the same problem. Bios not loading when GPU is attahced even though when GPU is detached computer runs fine. No system beep either. Got a corsair 600 watt power supply along with a ASUS B85 PRO GAMER motherboard and an I7 4790K. When the monitor is plugged into the motherbaord with a DVI no signal is displayed, however when plugged into thee GPU directly the message " PLEASE POWER DOWN AND CONNECT THE PCIe POWER CABLE(S) FOR THIS GRAPHICS CARD" is displayed. I have a attached two 6 pins into the GPU's 8 and 6 pin as instructed. GPU is attached into the PCIEX16_2 slot on the motherboard as the primary PCI is blocked. Can I just confirm that this is the same issue you had and that increasing the amperage of the PSU solves this issue.