So just recently changed out hardware due to GPU failure of old 780's and upgraded to 2x 1080's. Whiped the old driver and everything off and put on older drives because 378.66 was causing issues so at 375.70. Can run pretty much every games with small issue where the screen blacks out and loses connection to monitor during game splash screen and also when exiting game. This happens on every game. Using an HDMI cable. 
 
Specs
CPU: I7 6850K
Mobo: Asus sabertooth X99
Ram: g.skill ripjaw 32gb 3000mhz
OS: win 10 pro 64bit
 

It could also be that you need a motherboard bios update and / or windows 10. See if there is anything available for it.

I believe that I had this problem on my GTX 970, a while ago my GTX 780 SC had a problem where the VRM's exploded while playing EVE. I RMA'd the card and got a GTX 970 as a replacement. From day one this card has given me nothing but problems, it would randomly cause my screens to go black, and would come back to normal after 5 seconds or so. Some games would continue to run in the background while other would crash.
 
The only thing that I found to reduce the frequency of the problem was to lower the core frequency from its stock values. (No pun intended)
 
Anyways I just bought a GTX 1080 FTW DT, as I have already gotten fed up with the GTX 970 and my warranty ran out 2 weeks after my GTX 780 exploded. I am hoping that this new GPU will be good and wont give me problems.

The black for a second is normal when starting and exiting games.  The GPU is just changing refresh rates and/or resolution, the black flash could happen for something as minor as switching from 60Hz to 59.94Hz.
 
The entire computer crashing on the other hand is not.
 
Have you check your power supply voltages while running the game?  Do you still get the black flashes if running in borderless windowed mode?  Have you checked Windows Event Viewer for display driver crash recovery events?  What happens if you run with 1 GPU installed?  And last, have you tried a fresh copy of Windows (this probably wont help, but you know... troubleshooting)?

Quad5Ny
The black for a second is normal when starting and exiting games.  The GPU is just changing refresh rates and/or resolution, the black flash could happen for something as minor as switching from 60Hz to 59.94Hz.
 
The entire computer crashing on the other hand is not.
 
Have you check your power supply voltages while running the game?  Do you still get the black flashes if running in borderless windowed mode?  Have you checked Windows Event Viewer for display driver crash recovery events?  What happens if you run with 1 GPU installed?  And last, have you tried a fresh copy of Windows (this probably wont help, but you know... troubleshooting)?

Its not a quick flash its literally monitor says no connection about 5 seconds completely black then after about 3 seconds just goes black again then about 4 seconds of that it comes back. Does not do this at all in windows mode. It is hard to tell what causes the error each event is different so many errors. The issue its self is intermittent and also happens some times when alt+tab in and out.
 

Sajin
Time to test the cards individually along with different hdmi cables. How old is your psu?

PSU is from 2013 its this one . I'll check the cards solo tomorrow and different cables too but i wonder if it is the mobo...

So a couple of error reports. This one related to WOT (world of tanks)
 
1.
The password notification DLL C:\Program Files\WIDCOMM\Bluetooth Software\BtwProximityCP.dll failed to load with error 126. Please verify that the notification DLL path defined in the registry, HKLM\System\CurrentControlSet\Control\Lsa\Notification Packages, refers to a correct and absolute path (<drive>:\<path>\<filename>.<ext>) and not a relative or invalid path. If the DLL path is correct, please validate that any supporting files are located in the same directory, and that the system account has read access to both the DLL path and any supporting files.  Contact the provider of the notification DLL for additional support. Further details can be found on the web at .
 
2.
The NetTcpActivator service depends on the NetTcpPortSharing service which failed to start because of the following error:
The service cannot be started, either because it is disabled or because it has no enabled devices associated with it.
 
3.
The application-specific permission settings do not grant Local Activation permission for the COM Server application with CLSID
{3185A766-B338-11E4-A71E-12E3F512A338}
and APPID
{7006698D-2974-4091-A424-85DD0B909E23}
to the user NT AUTHORITY\NETWORK SERVICE SID (S-1-5-20) from address LocalHost (Using LRPC) running in the application container Unavailable SID (Unavailable). This security permission can be modified using the Component Services administrative tool.
 
4th is the same as above.
 
Saw this also before hand as a warning log 
 
The driver \Driver\WUDFRd failed to load for the device ACPI\PNP0A0A\2&daba3ff&2.
 
The rest are error logs.
 
Still looking for another hdmi i have hanging around somewhere.... single card still does the same...

genarus
Ok so already did the driver purge and install with an older one when this initially started and it did not fix it so that was ruled out.
 
Still did not replace the HDMI before i did that i uninstalled i guess the old monitor because i did change from a benq to a MSI. Also set-up the control panel as shown by Quad5Ny (except in 1080 =P).
 
And...it works there is no long black transition and rather seamless. I restarted my PC to make sure and the welcome screen to the OS came up instantly like it should and now alt-tab out of games is rather quick if no longer than 1 second. No crashing on previous games so it works as it should. Thank you guys for the assistance this is one less thing for me to worry about. Thank you Quad5Ny for the solution!

So what actually fixed your problem? Changing your monitor or doing what Quad5Ny suggested?