ATX Power Supply

Dan would like to get our old gaming pc going.  It's dead.  Mind you it's still not a bad computer.  I7 with 16GB ram.

Looking at the power supply.

This is the connector pin out
from https://superuser.com/questions/905705/atx-dell-psu-to-offical-atx-2-0-spec-pinout

Mains power attached.  No LEDs light.
On a good PSU lines 9 (purple) and 16 (Green) at +5V.  All the rest zero.
Our PSU - All lines zero
So we conclude ours is dead.
Getting in is not easy.  There are screws under the warranty stickers and screws under the main label.  Inside we see the components are tightly packed.  I think we see the reason for the failure - Dust and lots of it.