I traded my cousin some really expensive RAM that I happened accross for his old desktop, that he put his graphics card into that he swapped from his newer computer. If I plug the desktop into the wall and try to turn it on nothing happens. If I open it up I can see that the where the wire from the power supply plugs into the motherboard there Is a little light on. So clearly some power is getting somewhere…

How do I go about trouble shooting this, and what tools do I need? I assume at minimum a multi meter? Not really sure what to do, it’s been decades the last time I built a computer.