I am sorry to hear of your issues with your unit. This does seem to be a power issue that could be linked to the power supply, battery or the system board itself. Have you tried using a different power supply to power your unit and does this make any difference?
If this does not fix the problem then this could be a problem with the battery or the system board. In this case I would advise you call Medion Technical support on 0333 321 3106 to see if they can assist further and possibly book your unit in for a free assessment.