Thanks for your replies!
Yes, the phone can be switched to fastboot mode, the mode where I only see the Fairphone logo and the LED flashes blue, right?
There are not many steps I can follow. I can either end up in fastboot mode or in TWRP and whenever I reboot the system I end up there again.
I even inserted the SD card to my pc, copied the data for the last available update to it and tried to load one of the images in the folder, which may sound stupid, because I didn’t really know what I was doing, but I was desperate to try anything to render my phone usable again… I don’t have the faintest idea how I can proceed now…
Oh, latest news, now my phone seems to be stuck in fastboot mode. When I try to connenct it to my computer, I hear the windows jingle telling a device has been connected, but the phone doesn’t show up in Windosws Explorer. The device manager says, there is a “Kedacom USB device”, but I can’t interact with it.
Is there anything I can do now to proceed?