How long have you had the set for?
Also, are there any blinking lights on the front of the set?
Did this problem occur after a storm or power outage?
No blinking lights
after a storm
no signs of life at all - main fuse is good
The first thing you'd want to check is the caps on the power board for bulges or leaking. Any of these needs to be replaced.
Please only proceed if you have experience measuring live voltages on a circuit board level.
Next, use a DMM set to DC volts, find a common ground on the power supply and probe all of the Outputs for voltage (correct voltages will be stamped on the power supply at the outputs). Do this with NOTHING connected to the Power supply but AC power. If a voltage is missing/ fluctuating, then the power board needs to be replaced.
If the power supply outputs its rated voltages, then connect the other boards one at a time until one causes it to shut down. This board would have the short causing the supply to SOS, and would need to be replaced.
A good source to locate replacement boards is http://www.shopjimmy.com/ and http://www.discountmerchant.com/
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I do not have a source for that.