John wrote:

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.

To test an ATX PSU:

First, disconnect everything from the power supply (including MB.) Plug
AC cord into the rear of the PS. IF the PS has its own rocker on/off
switch, turn it ON. There should be +5v on pin 9 of the 20 pin connector
(+5vsb, usually a violet wire.) There should be 0.8v on pin 14 (PS-ON,
usually a green wire.) This is from an internal pull-up to the +5vsb.

Connect PS power leads to 1 or 2 IDE HDs (for a load). Jumper pin 14
(PS-ON) to pin 13 (ground, black wire.) At this point, fan in PS should
start spinning, drives should spin, and + 5/12v, -5/12v, +3.3v, and
+5vsb should be present at 20 pin connector.

Disconnecting pin 14-13 jumper should turn supply back off.

Further:

When your system fails to start, what is the voltage on pin 9? If it is
less than 4.75v, either a) the logic on your motherboard is shorting
b) your +5vsb is under powered, or c) your PS is bad. It is
most likely a combination of b) and c).

If your +5vsb is OK, measure pin 14 of the PS/MB connector. If it is 0.8v
(and the +5vsb is OK), the power supply should be on. If pin 14 is 0.8v,
the +5vsb is OK, and the PS is OFF, the PS is bad. If pin 14 is 2.0v, the
power supply is being told to stay OFF by the MB. If depressing the front
panel ON/OFF switch does NOT lower pin 14 to 0.8v (and the +5vsb is OK),
then the problem is NOT the power supply, but rather MB related.