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#31
You DON'T bridge the purple and black wires! The purple wire is the +5VSB (StandBy) line, and all I wanted to know was if there was actually any power present on this line and what its value is.
I note that unconnected there is 4.56V present, but connected only 2.25V. For the latter reading, is the system powered on or off?
Disconnect all peripherals, especially those that are USB, and also disconnect any that plug into motherboard headers (including FireWire, if present). What voltage do you get on that line now? If you monitor it as you disconnect things, you might even find the culprit (it could be something as simple as the mouse). Something somewhere is causing that voltage to drop to a level where it cannot power the logic circuitry that controls the function of the power button.