I'll be more specific... there's a component that's literally going through the grommet... what you have is to verify with another computer that works well all the components separately to isolate the one that's failing.
As I assume you don't have said computer to test with, the solution of taking it to the computer store is the right one because they have the tools (understanding another computer as tools) to verify that it's wrong.
Sometimes it's a silly thing but with what you've tried I would say that unfortunately the motherboard has all the odds of being screwed up or half screwed up... especially if it's second-hand.
Okay, thanks.