GPU not being seen on a build that has been running fine until now.

[MayorPotatoSalad]

Recently my while using my computer I was screwing around watching three movies on all three of my monitors (context not important) when my computer froze but unlike a normal freeze the screens went black and did not come back on. Tried all the obvious things, (windows d, Ctrl alt delete etc) but the screens remained black while the actual computer seemed fine, fans were still spinning, LEDs were all on. I resorted to holding down the power button for a forced restart but when I tried turning it back on again there was still no image while the computer was fine, including postcodes, something I did not check at the time of original error. This was about 2 hours ago and I have left it for a while, tried using onboard graphics, unplugged my monitors, plugged them back in to different ports on my GPU, checked the input on the monitors. Just tried again with onboard graphics and managed to get a picture. My computer no longer acknowledges the presence of my GPU and I have no idea what I can do. When I try and boot with the display cables plugged into the GPU the, Boot_Device_LED comes on, something that does not occur when booting on onboard graphics. If anyone has any ideas or tips they can give me PLEASE help, I am freaking out about what to do...   

System is custom, with parts as follows:
4790k CPU
GTX 980 GPU
Asus z97 Pro (WiFi AC) Motherboard
EVGA supernova 750w PSU
Custom water cooling loop 

[Deletive]

Try reinstalling drivers with onboard. that would be my first guess.

[theereal]

Recently my while using my computer I was screwing around watching three movies on all three of my monitors (context not important) when my computer froze but unlike a normal freeze the screens went black and did not come back on. Tried all the obvious things, (windows d, Ctrl alt delete etc) but the screens remained black while the actual computer seemed fine, fans were still spinning, LEDs were all on. I resorted to holding down the power button for a forced restart but when I tried turning it back on again there was still no image while the computer was fine, including postcodes, something I did not check at the time of original error. This was about 2 hours ago and I have left it for a while, tried using onboard graphics, unplugged my monitors, plugged them back in to different ports on my GPU, checked the input on the monitors. Just tried again with onboard graphics and managed to get a picture. My computer no longer acknowledges the presence of my GPU and I have no idea what I can do. When I try and boot with the display cables plugged into the GPU the, Boot_Device_LED comes on, something that does not occur when booting on onboard graphics. If anyone has any ideas or tips they can give me PLEASE help, I am freaking out about what to do...   

System is custom, with parts as follows:

4790k CPU

GTX 980 GPU

Asus z97 Pro (WiFi AC) Motherboard

EVGA supernova 750w PSU

Custom water cooling loop 

Have you installed the latest drivers? Have you opened your desktop and checked that everything is porperly connected?

[MayorPotatoSalad]

Have you installed the latest drivers? Have you opened your desktop and checked that everything is porperly connected?

Just un-installed all Nvidia graphics drivers but when trying to install the latest ones again I am unable to do so as the computer does not recognise that I even have a graphics card installed. I am looking at the computer as I type this and absolutely nothing is abnormal, both 6 pin power cables are plugged in both to the GPU and to the PSU and the card seems firmly inserted into the PCIE 16x slot on my motherboard.