Dual monitors shut off pc keeps running

[glenmic096]

Hi, since yesterday both monitors shut off and lose signal while pc keeps running in the background. The sound keeps going but for few seconds more and then stops. Then i restart pc and everything is back until it does it again. Yesterday, at one point, the monitors kept shutting down everytime im in a menu of a game, i turned off the PSU switch and today switched the psu back on and did it after few hours instead of instantly. Everything was working perfectly find until yesterday. What could it be please? Thanks

p.s Temperatures are all fine

my rig:

Asus Z87 plus C2
I7 4770K (oc 4.2ghz)
16gb ddr3
GTX 1070 8GB
Monitors: old Asus and BENQ XL2411
PSU: Corsair 750w

 

[hang-the-9]

First step, reset all speeds to stock. Could be failing power supply, maybe the video card as the two most likely issues if system still does this on normal speeds.