Hi siggi
Thats a strange one. Have you tried connecting it to a DIFFERENT PC/Laptop? If you have flashed it there should be few possibilities for the software on the Beaglebone to go wrong, and rather more likely seems the host PC is playing up.
I’d try a separate computer (and use a different mini USB cable for good measure) to get it to connect. It might be that your current computer has for some reason blocked it with antivirus or such, though I have not seen that happen particularly frequently.
Harrison