Can not open Photoshop Elements - always Serial Number window comes up

Hello, when I try to open Photoshop elements i am asked to enter my email and password and then the system asks for my serial number. I have entered it but after some seconds the window asking for the serial number comes up again. I am runnign in circles.

The Serial number is correct (and the same works for Premiere fine) but I have no idea now?

Does anybody know a solution ?