I have an old HP a1540n desktop. I was thinking about selling it, so I decided to throw it into a nicer tower first (the case it was in is DESTROYED!). I tested the computer, and it booted up.
I took it apart then, and reassembled it into the new case with a new PSU that was 350W.
Once I finished putting it together, I turned it on.
I switched back to the old PSU, because the new one does not have a residual energy light, so I couldn't tell if the PSU was faulty or something else.
The light came on, and when I pressed the power button the PSU fan began to spin for a microsecond, but no other signs of life showed.
I tried switching the power button from the original case incase the button was somehow faulty, and the same thing happened.
I unlugged EVERY component besides the PSU, the MOBO, the bios battery, and the processor/processor fan.
I'm assuming it's screwed, so don't bother posting if you're just telling me it's screwed.
I decided to post this on the off chance somebody may know something else I can try to get it to work.