title_body: How do I delete an undeletable book from my Kindle?
upvoted_answer: Try deregistering and reregistering your Kindle:
  
  
  Have the Kindle online through Wifi.
  Press Menu (three lines stacked).
  Press Settings.
  Press Registration.
  Press Deregister Device and confirm it.
  Wait a few seconds for it to take effect.
  
  
  Repeat the above steps, but pick to register instead of deregister.
  
  My collections had to be added back to the Device from the Cloud, and I had to set the parental control password again.