Joined: 7-July 03
From: Tropical Island
Member No.: 47802
Xbox Version: v1.6d
360 version: v5.0 (360S - trinity)
In mu repair business I have come across alot of dead XBOX's or ones like yours shutting down for no reason.
And all have been the solder pads around the black AC power plug in the back of the power supply unit which have got cracks around them or the pin has pushed away from the solder pad on PCBoard.
Very easy to fix, just open your XBOX, and then remove the two screws holding the power supply, and push it back a little bit and then lift it up away from the case.
Flip it over, and look at the very back you will clearly see where the power plug two solder spots are, just use a 30watt soldering iron heat up each spot for at least 3 to 5 seconds, and if needed add a little more solder.
Put the PSU back inside your xbox, and try out your system. It should be working great now!