Power Supply Gone Bad?

Quick question for you all. I have been having some problems turning on my
PC, sometimes it works sometimes it doesn't. I notice when my power cable is
plugged into my power supply that I do have a green LED on my motherboard
and when it's unplugged the light goes off. Is it possible for the LED to
come on if the power supply is dead?
I have checked the power button and it looks to be wired fine. I've had my
power supply for about 2 years now and am just recently running into
problems with it it seems. Any help would be appreciated as I dont wan't to
spend any money on a new power supply if it's not the problem. Oh ya and my
PC doesn't even POST.

J.