PC Freezes with Looping Sound

It seems I cannot get the PSU to start without the mobo. I've tried shorting Pins 15 and 16 as suggested in the guide to get it started, however the PSU doesn't start no matter what I try. I took a good look at the Motherboard connector and noticed that Pin 8 is completely missing. Knowing this, it might just be a good idea to replace it anyway. I don't know why a pin is missing altogether, however it cannot be a good thing. It's not like the pin broke either, the entire wire is missing, it's like the PSU was made without it. The pin chart that goes with that guide says:
8 PWR_ON Gray Power Good
I'm unsure what that means, since it does Power on, but it missing it cannot be the best of things.