PC won't boot - PSU failure?

[OuPeeNoob]

Hi,

I've had an issue with my PC a few weeks ago. I left it in sleep mode, but when I came back to switch it on I only heard the fans working but the screen wouldn't switch on.
After doing a bit of research online I assumed the motherboard may be broken and bought a new one.

Now with the new motherboard I have encountered the same problem. Especially switching the PC off without switching the power at the back off will result in starting the PC with the fans working only. I can get it to start when I unplug the power cable and press the power button on the front for 30 seconds and wait another hour before attempting to boot.

I currently have a Corsair CX600W and a GTX980, and I don't know if this is enough power or whether the PSU is simply about to die.

Can anyone let me know if this could be due to my PSU being broken or any other component failure?

Thanks in advance for your help.

 

[snips86x]

If you take out the BIOS battery for 5-10 mins, does it boot then?
Also, remove the GPU and use the on-board to see if it boots this way.

I used to have the same issue with my 980Ti, had to disconnect the monitor power or output cable to bring it back to life.

 

[OuPeeNoob]

I tried resetting BIOS (ie. taking out battery and shortening the two pins) at first, but I really need to wait that one hour at least before successfully attempting a restart. Waiting and discharging residual power will also work without resetting BIOS.