Aquaris M10 Ubuntu does not start

The tablet does not start successfully. The (white) screen "powered by Ubuntu" appears for approx. 1 second, then the screen turns black, and after 6 seconds the start-procedure begins again. Pressing the power-button has no effect (bot for a second, and for up to one minute). Pressing power plus loudspeaker interrupts the start procedures, but once one of the buttons is released the system will begin starting as described above. Any options for a reset?

Kind regards,
Stefan Weingardt