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My computer is almost 3 years old by now, and last night I noticed it turning on and off randomly for a few seconds, multiple times. I tried to turn it on to investigate, but it didn't react to the power button being pressed. Naturally, I checked the PSU voltages using a multimeter (they were fine), then I proceeded to take the motherboard out and turn it on outside the case. It turned on without problems, Windows booted just fine. Then, I reassembled everything, connected the front panel connector (there are no separate wires for power button and LEDs, it is all in one connector). When I pressed the power button, the PC turned on, then after 5 seconds it shut off. I became frustrated, and disconnected the front panel connector from the board, and touched the power button pins with a paperclip. Guess what, my PC turned on and there were no problems at all. I tried reconnecting the front panel connector again, but it did the same thing. Then, I checked the power button pins on the connector using a multimeter, and they only shorted when the button was pressed (that's OK). In addition, I checked the power and disk activity LEDs to see if they are shorted, but those were fine too. It does not have a reset switch, so it looks like I checked all pins. Now, I am genuinely clueless, I really don't know what's the problem. Does anybody have an idea, what to do in this case?

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    Take it to a repair shop for proper diagnosis.
    – DavidPostill
    Dec 25, 2020 at 18:56
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    It definitely seems likes your wires are shorting together somewhere. Maybe, its the PCB inside the case that is shorting. Either that or your power button is simply worn out from use or defect.
    – cybernard
    Dec 25, 2020 at 20:12

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You've done a good job of diagnosis. Look for physical damage to the wires between the power button/indicator sub-PCB and the case, and to that mini-PCB, and for distortion of the case when cover is attached that might cause undesired contact. Check the resistance of the each terminal of the connector to ground (i.e., the faceplate); a short to ground might be causing the issue. Also check for hairline cracks in the circuit traces of the main PCB that might be flexed by attaching the cover.

At the worst, you could cobble together a two-pin connector, or solder wire to the pins, and connect the other end directly to a new switch.

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  • Thank you for the suggestion! I didn't think the front panel PCB could be the culprit. I ended up making a new one using some perfboard and a new button, and now it works perfectly.
    – lorinet3
    Dec 26, 2020 at 13:50

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