ok so now i just read your entire post and realised that my post would be of no help whatsoever............
If i were you, id just use the same ole pushbuttons that came with the computer =\
But now, editing for a second time, i've reread your post, and i seem to realise something new each time!!
So heneway, is the switch ya picked up from the shack a toggle switch or pushbutton switch? Cuz if its a toggle, your computer will shut down after 5 seconds, the mobo is designed to start up the computer if it is off and the power button is pushed and released, but if its held for 5 seconds (might be 6), it shuts down the computer. So, if its a toggle, it will be interpreting the constant closed switch as you holding the power button to shut it down, as opposed to just tapping it to turn it on. Try just flipping the switch for a moment then shutting it off.