Recently one of my PCs has developed a resistance to powering up. I have not been able to single out whether it is the motherboard or the PSU that is the problem – at worst case it could be both. However because the PC is running mostly 24/7 it has not been a big enough annoyance to replace any parts. It only fails to powerup if it has been disconnected from the mains.
With a paperclip (or piece of wire) it is very simple to jump-start the PSU, and this solves the rare occasions that I do have to shutdown the PC:
On the PSU’s cable to the motherboard there should be a single green wire – this is the poweron switch. To jump-start the PSU simply short the green wire to a black wire (any of the black wires). If you leave the short in place the PSU can never shutdown, so for safety sake you should remove the wire after starting the PSU.