How to Diagnose a Dead Desktop PC: Step-by-Step Guide

Symptom 1: Nothing happens when you press power

1. Check the obvious: wall switch, power strip, kettle lead seated firmly at both ends, and the PSU's own rocker switch set to "I".
2. Test the outlet with a lamp or phone charger.
3. Paperclip test the PSU: unplug everything, short the green wire to any black wire on the 24-pin connector with a paperclip, then switch on the PSU. If its fan doesn't spin, the PSU is likely dead.
4. Check the case power button: short the two power-switch pins on the motherboard with a screwdriver. If the PC starts, the case button or its cable is faulty.

Symptom 2: Fans spin but no display

1. Check the monitor input — is it set to the right source? Try a different cable.
2. Reseat the RAM: remove sticks, clean contacts gently with an eraser, reinsert firmly until the clips click. Try one stick at a time in each slot.
3. Reseat the GPU and its power cables.
4. Listen for beep codes — consult your motherboard manual (1 long 2 short usually = graphics; continuous = memory).
5. Reset CMOS: remove the coin battery for 2 minutes, or short the clear-CMOS jumper. Corrupted BIOS settings are a common cause.
6. Try onboard video: remove the GPU and connect to the motherboard's HDMI/DP port.

Symptom 3: Powers on then shuts off immediately

• Overheating CPU — check the cooler is mounted firmly with thermal paste.
• Short circuit — check for loose screws behind the board, damaged USB ports.
• Failing PSU that can't sustain load.

Symptom 4: Starts but freezes or blue-screens

Run memory diagnostics (Windows Memory Diagnostic or MemTest86) and test the drive — see our hard drive guide. Check temperatures with HWiNFO.

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