Turn off the PC and unplug it from the wall
Open the case and inspect the power supply unit for damage, dust, or burnt smell
Check that all power cables are firmly connected to the motherboard, GPU, drives, and fans
Verify the PSU switch on the back is set to the correct voltage if applicable
Plug the PC into a known working outlet and power strip
Press the power button and check whether fans, lights, and drives start
Use a PSU tester to check voltage outputs
Use a multimeter to test the PSU rails if you know how to do so safely
Test the PC with a known working power supply
Check the motherboard debug LEDs or beep codes for power-related errors
Inspect the 24-pin motherboard connector and 8-pin CPU connector for loose pins
Remove and reseat the RAM, GPU, and power connectors
Check whether the PSU fan spins when the system is powered on
Look for random shutdowns, restarts, or failure to boot
Compare the PSU wattage to the system’s power requirements
Replace the PSU if it fails testing or shows signs of instability