Asus ROG Zenith Extreme AMD Threadripper 2920x 32GB G.Skill F4-3200C14Q-32GTZRX 2x Asus 1080ti Poseidon Corsair AX1200i
My main monitor is an Acer Predator XB1 27" WQHD IPS with 165 Hz and nvidia G-Sync (XB271HU)
I have a secondary Full-HD monitor which is a cheap iiyama IPS that works fine.
Before I upgraded my system to the aforementioned one, I used to have an asus X99 E-WS with an i7 5930k and 32GB of Kingston memory, same set of GPUs and screens. Everything was working perfectly fine.
Now I have a VERY odd issue where if I plug in my gaming monitor (the Acer Predator) into my GPU (no matter which of the two or which DP port), I can't switch on my PC. It just flicks on for a split second and turns off. No boot attempt, nothing. It's as if overcurrent protection is triggered. After unplugging the monitor and turning on the PC, it boots a few times, but gets into windows just fine. It gets weirder: When I now plug in the monitor while the PC is running, everything is just fine, the monitor gets recognised and works! Unless I shut down the PC and try to turn it on again, then I have to unplug the DP cable from the GPU for the PC to turn on. Restarting the system on the other hand works with the monitor plugged in.
I've tried the monitor on another PC and it doesn't have this issue, only on this system. I also plugged in the EZ-Plug on the Zenith Extreme MB, just for good measurement.
Try plugging in the Acer in the first display port of the first card and see if the screen appears and loads into Windows. Later on plug the 2nd monitor to the same card and you will have to adjust the setting's in the Nvidia control panel. Test by rebooting the system. If you have chosen the setting's before rebooting for example, that it will load on one screen or it will load on two screens, it shall be done that way. Let us know.