I found the mistake. The service configuration of FOG contained the fully qualified name as hostname. I replaced it with the IP address and it worked and the menu looked different too.

@sebastian-roth Yeah, there was the wrong path in it. Thank you very much.
So it’s not a hardware problem.

How did this happen? I installed it twice on the system. The first time I hit Enter when I asked for the database password. But that was wrong. I then uninstalled it and reinstalled it from the front. Maybe something went wrong. In particular, uninstalling was very fast compared to installing.