Phone doesn't start

[Stefan]

@Matthias2

As I try to start it, just the screen with the “Fairphone” lettering appears.

I think your phone boots to Fastboot mode (reference).

@rootboi

Press and hold down the Volume down button while pressing the Power button

Is there any pressure to your volume down button? Can you take off your FP2’s cover and try to boot (=start) your phone again?