Issues with turning the PC ON

Hello guys,

I am having a very annoying issue with my PC and it seems to be getting worse by the week,

Few months a go when I pressed the ON button my PC had a 5 second delay before it turned on ever since then it has been random, so when I press the ON button it would sometimes turn on the same second as it should and sometimes it would take 5 - 50 seconds.

Lately that was not enough to start the PC I now need press the ON button and flick the 0-I switch at the back of the PSU and that starts the PC. BUT for the past few weeks it's gotten really bad I would constantly need to press the ON button and keep flicking the PSU switch back and forth.

I switches the buttons to use reset button as the on button to see if it would help but it didn't so the issue is not the ON button. Somehow my guesses are that it's the motherboard.

Not sure what to do any more, any suggestions?

Thank you.

CPU: i5 2500K @ 4.0Ghz

Motherboard: Gigabyte P67A-UD4-B3

Power Corsair: AX850W PRO GOLD

Ok I tested the PSU on my friends PC and it refused to boot.

So just to make sure I connected the PWR ON and GND pins and had a fan plunged in via molex and turning the PSU on at the back did nothing it didn't spin any of the fans.

Is it safe to assume that PSU is dead?