Yes the switch on the back of the PSU. I got the Corsair TX650 as replacement. I tried the paperclip method on mine and it would power on but not when it was connected to the motherboard, something to do with the power OK circuit.
Yea I just jumped it with a paperclip and it came on too, but no luck while its actually connected. But all in all it does in fact seem like a PSU issue like you said, I'm glad it's not something more severe. Thanks for the help man..... really appreciate it.