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.
The power supply connect with the motherboard in more than one place. If “the wire from the power supply plugs into the motherboard” is a thing, that may be your problem.
Unplug anything that is optional (that includes disks and stuff that you have more than 1, like maybe memory sticks) and try to power the computer. If it works, replug stuff one by one.
As BigMikeInAustin said, remove everything and plug it again. I’d add to get a paint brush and clean stuff a bit in between if it’s dusty. Make sure to clean plugs and contacts, try not to clean electronic components.
Try to remove the board’s battery for a few minutes and turn the computer on again. Some times that’s enough.
Also, turn the computer on for a minute or two, turn it off, unplug everything, and touch the surfaces to see if they are hot. Try not to touch any printed circuit board.
Second unplugging all optional components (RAM is not optional) - and the video card in particular. A card that pulls more power than your power supply can provide could do exactly what you are seeing.