The unit does not need to be switched on via the button, it switches on automatically when you charge a device. Have you tested the different connections to see if you can charge a device? And also with different charging cables?

If yes, then the powerbank is probably defective. Unfortunately, this happens frequently (at least to me). I have already sent this powerbank in twice for repair under warranty (within a year).

I would try using different USB cables on different sockets. Even if only one socket is "dead", it would be a warranty case. If a private cable is defective, simply replace it ...