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#21
The power button on the case is a momentary contact normally off switch. The contacts are only closed (on) while the switch is depressed. It is conceivable that its faulty and the contacts are making contact , maybe intermittently, when the switch isn't being pushed. That could cause the PC to turn on by itself. If windows is set to shutdown when the power button is depressed (power options) it could also cause the PC to shut down gracefully. The case reset button works the same way as the power button. If you get your motherboard back and the problem is still there unplug the cable for the case power button and swap it for the reset button. Leave the power button unconnected. It you problem goes away it was the case power button. I'm more inclined to think its probably the circuit on the motherboard that the power button connects to that is faulty. Only time will tell though.