I would try to take the SD card out, format it through a card reader directly on a computer and put (again ?) the latest firmware on the empty card from the computer. The link to the latest firmware can be found on the wikipage
https://wiki.mobileread.com/wiki/Digi...e_applications
Put the card back in, start up and see what happens.
Unless there is some serious hardware problem, I can see no reason why this shouldn't work .... good luck!