I was indeed aware of those potential idiosyncrasies, having suffered from different power cables to a video card in another system, several generations ago. But this not the case now. I only use the original Corsair cables. Anyway, I have repackaged the mobo now and will be exchanging it with...
Checked the socket and nothing appears wrong or bent. The only connections are two Noctua fans (that work OK) and the 20 and 8 pin power cables. Looks like a DOA board. I'll start the RMA. Thanks for your help.
Just installed this mobo with an i7-5960X CPU and 8 x8GB G.Skill Ripjaws F4-2800 memory modules. PSU is Corsair AX-1200, known to be good.
Video card is Zotac GTX 980Ti installed in PCIe slot 1. Turn on the power and QQ code shows 00. The mobo, video card, fans all work but nothing happens...