At the end of the game, you get a computer. When you press 1, either a code or an inscription appears. To get the code, trust the man. I can do a tutorial later if it's too hard to understand.
Look, I take it you either have a bug or you're closing the game at the wrong time. I'm leaning towards the former. You should not have waited at all, there are two dialogues that last 1-2 minutes. Try downloading a new version. If after 5 minutes, this window does not close automatically or you have a black screen all the time, write again.