I have a similar "problem" with my Literati. Turns out that some of the
ebooks I download are not EPUB format, but PDF format. My Literati
segregates them into their own area, called "DOCS", instead of the library.
I don't know if this is true with Nooks or not, but your problem sounds just
like this. My suggestion is to check the ebook format, and if it's not
EPUB, then look for it in another tab on your Nook. You would know that it
did not succeed in the download, so it's there somewhere....
Regarding your problem you can try following steps.
Delete following folder from your computer.
C:\Documents and Settings\(UserName)\My Documents\My Digital Editions\restore.
Now try to locate books in your Nook library
I hope this will help you!!!
If you can see the file when you look at the files on your Nook on your computer, the solution should be simple. While in My Library (MY B&N Library), choose My Documents or scroll to My Documents and select it. Now you should see your downloaded book. Hope this helps.