i accidentley switched the red switch on the power supply unit on my dell optiplex tower and i heard a bang so i got a new power supply unit ,same part number put it into the tower and the tower still wont come on have i done some other damage
It's likely that the motherboard and possibly other components are damaged also. There's really no good way to test parts in that computer, so the best thing to do would be testing each component one by one, if you have an extra computer that is compatible with those components. It may not even be worth the time and effort to try to fix it though. Good luck.