Question Monitor suddenly "no signal", PC running OK.

[Pez Clarke]

Monitor suddenly went off tonight, black screen, "no signal" fault on the screen.
PC, fans, lights etc was still running and I could still hear the game in the background.
Did a restart, no good, checked monitor and cable on wife's laptop, both working on that but not when plugged into my PC.
So I'm thinking gpu or psu? Both about 4 years old, any ideas of what my next step would be? How do I check them as I have no spares of either?
Thanks in advance

 

[Mikek26]

This problem is growing I have a gaming rig and all 3 of my monitors are saying no signal I have try'ed everything that I could find like removing bois battery switch ram went to one monitor then try'ed with another monitor took out my gpu and did a direct hdmi to motherboard and same problem