Question about ASUS ROG Maximus XI Hero WiFi

So I would say that almost all cards work here. Certainly all gamer cards. Try a different PCI-E slot.
Otherwise I would try the same as Insectman wrote. Have you connected both power cables 6+8 pin? If none of this works, there is probably a hardware fault.

I also had problems with the display port on my graphics card at first. The mainboard kept whining that there was a hardware error, even though the graphics card was lit up and the fans were running at full speed. The solution was to set up the PC via the hdmi port on the mainboard and install the latest nVidia driver in Windows. After that, it worked for me without any problems.
Maybe this approach will help you.