No screen

[Muzzy2002]

So my PC was randomly shutting down and I found out the 24pin wasn't plugged fully in so I did that and now my PC will start up and everything but have nothing on the screen the monitor doesn't even react to it like usual. I have already tried resetting CMOS integrated and gpu graphics i also swapped around the ram and made sure that's not the issue which it isn't I'm certain it's not the processor as the system stays on and such and the temps were fine when I had it on so I think im only left with the psu and the mobo so would you guys say it's the power supply which is faulty or the motherboard but the motherboard lights up and my cpu fan is working so I'm guessing psu what do you guys think any help appreciated thanks.