Stupid question, but you have got all power management and sleep functions turned off? I run my monitor from the iGpu, and hdmi dummy plugs on the Pcie cards. I had a similar issue when I first built my rig, turning off all power management, and sleep functions cured it for me.
so weired this is driving me insane i want to shoot my self i turned power saving features off at to my surprise it boot straight up updated windows install latest nvdia driver everything allgood.. shut down system install 2nd card turn system on no display signal. remove 2nd card turn system on no display signal ive set up multiple rigs with these boards before and have have had very little trouble but this one 3days of trying now im over it
H81pro btc
G1820
4gb 1600mhz
120gb samsung sdd
1050watt Seasonic gold
5x1070s struggling to get it going with one......
5x usb powered risers with molex