Both monitors lose signal after playing for awhile

[Azziel]

Hi there, I have been having this issue with my computer, ill explain what happens and the steps I have taken so far in hope you guys can assist me.
So while gaming mainly GTA V after a good 10-15 min both my monitors lose signal, I can hear sounds and my Skype call doesn't shut down, so all it happens is that I dont have signal.
Now this used to only happen playing GTA, I could play LoL, Dragons Dogma and FM 2016 for hours without a single crash. But then today while playing LoL it crashed.
So now the steps I have taken so far:

• 
  I have check the temp, constant 50C while playing.
  Applied new paste to the Cpu
  Check every cable if its well connected
  Installed a older driver ( i had the latest one )
  Change the hdmi cable on the monitor.
  Rearrange the fans for optimal air flow
  Cleaned the PC of dust (it was pretty clean to begin)
  I swapped the power cable on the GPU (i was using an adapter without needing)
  

That's all the steps I can remember, I am seriously lost here I dont know what more I can do, I cant test a different GPU because I dont have one and I cant replicate the problem accurately since sometimes it does it in 10min sometimes doesn't do it at all in GTA.
It can be the PSU but its not that old of one and its a 750W power one.

These are my specs:

Intel Core i5 3350
Nvidia GeForce GTX 960 Palit
8GB Ram
Nox Urano VX 750W

 

[Azziel]

quick edit: been playing GTA V for 2 hours now and nothing no crashed or anything, but since i cant replicate the problem i am not sure if its fixed or not