During the final step of building a desktop, a technician plugs the system into a known-good outlet. A green standby LED on the motherboard lights, but pressing the case power button produces no fans, no drives, and no POST tones. The technician has not yet screwed the side panel back on. Which internal check is the BEST next step to restore power to the system?
Verify the case power-switch cable is attached to the proper pins on the motherboard's front-panel header.
Move the power supply's input-voltage selector from 230 V to 115 V.
Reseat the 24-pin ATX power connector on the motherboard.
Replace the motherboard's CMOS battery with a new one.
Because the motherboard's standby LED is lit, the power supply is providing the 5 V standby rail and the 24-pin ATX connector is seated. If the system will not start when the front panel switch is pressed, the most likely cause is that the momentary power-switch lead is not connected to the correct pins on the front-panel header, so the PS_ON# signal is never pulled low. Re-connecting that cable is therefore the logical next troubleshooting step. A dead CMOS battery will not prevent power-up, the input-voltage selector would keep the standby rail from lighting, and a loose 24-pin connector would already have been revealed by the lack of the standby LED.
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What is the PS_ON# signal, and why is it important?
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What does the standby LED on the motherboard indicate?