Thank you everybody for your answers.

Reflashing is difficult without a working usb port.

I can't start any application and any terminal:

The "knight rider" shows up and during this time a dialog appears that asks me if I want to switch off the offline mode on to the online mode.

...But the dialog is not responsive and blocks the whole booting process.


... what I would like to hear would be "You hit these three buttons during the booting process and this dialog is skipped." But I think there is no hope.