If you log onto your BN account, go to the eBooks tab, then over on the right side of the screen you should see the "Archive" option. Click on that and there you will see the "deleted" books.
This is where you will find all of the books that you delete from your nook. You can re-add those books to your library.
Once you buy a book it is never really deleted, it is just added to the archive.
Hope this helps!
I dd as u said, & it worked for two of the books, buy not for the third. Any ideas???? I have tried 3 time to download it again, but it still doesn't show up in my library.