$129 diagnosis. sheesh. talk about easy money :P
You can test the power supply by taking it out, unplug the mother board connector and with the power supply plugged in short the green wire to one of the black wires. If the power supply still works fine it should fire right up as long as you keep those two wires shorted.
If somehow something else in the computer went haywire and is showing the PS a short or something it will also sense this and not turn on.
I had the PS in my desktop die a few months ago, it worked fine then i shutdown the computer and went to turn it back on and it was dead.
