Your motherboard should have 2 pins (check your user manual) that, when connected, turn on your PC (at least that's what I'm assuming you're trying to do). A computer case's power button is just a momentary switch. Its normally-open prong connects to one of the pins, and it's ground to the other. When the button's pushed, puter comes on. An arcade microswitch is well suited to this sort of thing, and is connected the same way.
