I'm not in High School but regardless you don't take away positive activities that induce hard work, leadership, and comradeship. Its counter-productive.
I agree with the limiting the computer to certain hours. I also think it's pointless to punish the kid for trying to get away with keeping the computer. You forgot to ask him for it. That's your fault. The fact that he didn't bring it to you is irrelevant. It is your job to enforce the punishment. I would NEVER just wave a white flag and hand over something like that. If my Dad came to me repeatedly and asked me to give it back, would I back talk him? No way. If i fuvk up and get punished that's my fault. But you can't blame him for your mistakes either.
Him disappearing for the night is unacceptable. You should have called the police and told them to pick his *** up and bring him back home in the backseat of the cruiser. That would scare the shit out of him. If not then he's a lost cause and you tried.