Wondering if anyone else has experienced a similar issue:
 
System specs: Windows 8.1 x84 (6.3.9600), GTX 1080 FE, 368.39 drivers, Xeon 1650 v3 CPU; ASRock X99 WS-E motherboard, Crucial CT32G4RFD4213 ECC RDIMMs x5, BIOS v1.80, (BIOS 3.0/3.2 has other issues with Xeon v3 processors; meant for v4 processors)
 
When card has display inputs plugged in and returns from sleep, monitor(s) power up and return with either a black screen, or with the Windows 8.1 lock screen, but no text on it. Keyboard and mouse still respond, however system remains in this state and is not possible to log in again, CTRL+ALT+DEL is also unresponsive. Same behavior exists with 1 or 2 monitors plugged in via DP and HDMI to GTX 1080, or with a different monitor plugged in via DVI and different keyboard/mouse. Also switched DP slots on GTX 1080 card with just 1 monitor plugged in, same issue.
 
If GTX 1080 card has no display inputs plugged in (using a Quadro K6000 or GTX Titan Black in a secondary PCI-E slot to drive a display) then system resumes normally from sleep.
 
Further, suspend/sleep behavior is as expected (no black screen or hangs) when using Ubuntu 14.04.4 on same hardware (Quadro K6000, GTX 1080 driving displays) and 367.27 drivers, so suspect this is a Windows driver issue.
 
Finally, as last troubleshooting step, if a GTX Titan X is replaced in the same slot as the GTX 1080, it does not experience the same return from sleep issue with the same 368.39 driver, further pointing to a driver issue with GTX 1080 card.
 
I submitted pretty much this same text to NVIDIA as a bug report... will see what they say, but as my return for replacement period is near, wanted to see if others had this issue, or if it's isolated to my particular configuration.

After doing extensive testing, turns out a O/S reinstall (same Windows 8.1 x64 w/ updates) was able to come back from sleep without issue. That being said, takes longer to come back from sleep than if I plug the display input to another card (e.g. GTX Titan Black), so perhaps there is some driver issue there. Just wanted to update on a solution.

If what EVGA tech Joseph doesn't work you might have to disable the PCI-E from sleep.

Thanks all for the replies.
 
@EVGATech_RayH I set "Link State Power Management" to off, but didn't see any improvement in the time the monitors active are after return from sleep, but I also didn't reboot since the change -- not sure if that setting change instant or not.
 
I actually had gone through the DDU bit with NVIDIA and it didn't improve anything in my original Win 8.1 x64 install. My only theory is that since that installation was actually from a previous system and then sysprepped, something left over was causing an additional glitch with the 1080 returning from sleep. I've installed a few programs I normally use, and so far I can return from sleep without issue, albeit a bit slow. The HDMI KVM I have actually makes it come back from sleep a bit slower when it is connected, but with the previous install that had the sleep of death issue it was disconnected and the issue didn't go away, so it wasn't the cause... just some software issue.
 
I updated the ticket I had at NVIDIA with pretty much this same info, maybe they'll see if there's some additional delay added by the GTX 1080 when it comes to wakeup from sleep compared to other cards (GTX Titan X, GTX Titan Black, for example)

I have zero issues with my Gtx 1080 with sleep. I have an Asus strix though, not evga