thank you for all the help you have given me. sadly i cannot report success or failure because i no longer have the tablet. the owner got impatient and no longer wanted to wait for me to find time to work on his tablet.
i see no reason why the installation from the windows image should not work. sadly, in the little time i had, i didn't even got so far as to install from the image. in the end the thing which gave me most trouble was the presumably failing power button which i needed to press for many seconds repeatedly to get to where i need to be to set things up so they do what i want. and since i do not know where the settings are i needed to restart the process often. and many times where i found time and patience to work on the tablet i gave up frustrated after several times of pressing the power button and hoping the button works and not knowing whether i didn't press long enough or the button failed.
so again thank you for the help and sorry that in the end i could not give a positive report back.
and a parting message: this device main input method was the touchscreen and the keyboard. but once the software (windows) failed the only input method left was the power button. if the power button fails you have nothing. and the tablet was not build to open and replace the button. do not buy such devices. do not build such devices.