Turn off the computer and unplug it from the wall
Open the case and locate the power supply
Check for visible damage, burnt smell, or loose cables
Use a paperclip or PSU tester to perform a basic power-on test
Disconnect the PSU from all components before testing
Bridge the green wire to any black wire on the 24-pin connector with a paperclip
Plug the PSU back in and switch it on
Check whether the PSU fan spins
Use a multimeter to test voltage on the 24-pin connector
Test the 12V, 5V, and 3.3V rails against expected values
Test the PSU under load if possible
Reconnect the PSU to the motherboard and components
Power on the computer and check for boot issues, shutdowns, or instability
Replace the PSU if voltages are out of range or the unit fails to start