To clarify, disconnect the speaker and see if any whining occurs around the power supply, just to rule that out. But I agree in that it's probably the sealed capacitors on the motherboard itself that need replacing. You might be able to replace just the leaking/bulging caps and get away with it, but ideally you will want to replace all the capacitors on the board.

Also wondering if that hard disk have a lid? Coz it's going to last about ten seconds as soon as dust gets in!