Used PC shows power but won’t start—what should I check?

Open the case and inspect it for cables or components that came loose during transport. Reseat the RAM and, if necessary, disconnect nonessential parts and try a minimal setup with the motherboard, CPU, one memory module, and power supply. If it was never tested before purchase, there’s no way to know whether the power supply or another major component was already defective.

If the case button or its cable is faulty, you can briefly bridge the two power-switch pins on the motherboard with a screwdriver to test it. Only touch the correct pins identified in the manual, and do not bridge random connectors. If the system still does absolutely nothing, the likely causes include a failed power supply, a loose connection, a motherboard fault, or a short.

A light by the Ethernet port usually only confirms that standby power is reaching the motherboard; it does not prove that the power supply can start the computer. Testing with a known-good compatible power supply is safer than opening the power supply or probing its internal wiring. Avoid the green-wire jumper test unless you know exactly what you’re doing, since incorrect handling can damage hardware or cause injury.

Start with the simple checks: make sure the power supply’s rear switch is set to on, try a different power cable or wall outlet, and confirm the 24-pin motherboard cable and CPU power cable are firmly connected. Also verify that the case power-switch connector is attached to the correct motherboard pins. The motherboard manual will show the exact front-panel header layout.