You have hard-reset it before, right? Worth trying again before giving up anyway to reset it to factory settings:
  • Make another backup of the files and folders if you want as the reset will also remove all your personal user data
  • Power the device completely OFF
  • Press and hold the user button, located just below the power button
  • Press and hold the power button while continuing to hold the user button
  • When it powers on, release the power button but keep holding the user button for the moment
  • A message will appear asking "Do you really want to erase all user data?", at that point also release the user button
  • Select "Erase" on screen