I'm running an up to date NVIDIA version 8.1.790.0, on Windows 10, with an EVGA GTX 980 Ti driving two ASUS 4k monitors through DisplayPort.
All works well until the system goes to power save if I have left the monitors on - then I move the mouse or touch a key and the system wakes, but only with one monitor. In graphics properties, only one monitor is available.
I can then go back into NVIDIA control panel, Set up multiple displays and I get the option to check the box for the 2nd monitor, and when I hit Apply changes, the 2nd monitor is enabled, and as long as I move something onto that monitor it remains on until the next time the system sleeps - if I don't move a window onto that monitor it sleeps again after 30 seconds or so.
I have googled for solutions, and looked on the NVIDIA forums but had no joy.
I have also seen this question but the top answers refer to AMD or Quadro cards (with different functionality)