[PLUG] computer will not start (2X)

[Denis Heidtmann]

Narrowed down to a problem with the standby 5V.  The MB has an LED
which indicates that the standby 5 volt supply is on.  This LED
flashes when the problem occurs, indicating overcurrent, shutdown,
repeat.  The two times this has occurred it went away spontaneously
(Nothing I was doing can be said to be the cause for the problem going
away.)  I watched the LED while unplugging back cables (keyboard,
mouse, USB, etc) one at a time.  Nothing changed the status.  Then
while doing nothing it suddenly changed--the LED became steady on.
Then the thing started fine.

The computer is often completely powered off--no AC to the power cord.
Other times it is off with AC on.  On the 2nd occurrence it was in the
latter state when I attempted to start it.

The PS is a 380 watt Antec.

I am open to suggestions on how to diagnose this problem.  My first
though is to measure the standby 5V to see if it is marginal.  I have
to see where is the safest place to put a probe.

-Denis