Default Protab 3 - broken??

Hello,

my mother owns a ProTab 3 XXL. Since yesterday the tablet is not starting any more. I tried the reset button and several combinations with the front buttons.

i also checked the voltages:
- charger: 5,2V
- battery when charger disconnected: 4,3V
- battery when charger connected: 4,3V

is there something wrong? How can i fix the tablet?

thank you very much,

machinE