I've updated my RPi3 to v8.1.0 beta without any problem. After a while the system stucked, so I rebooted by disconnecting powercable.
Now I get an error message during boot that there is no device to boot from. I checked the micro sd with an usb-adapter and it seems to be ok. It is still readable with all files on it.
Anyone got an idea what to do until I do a fresh installation?