Hi!
If you have saved the data folder (library name.Data) that belonged to the library, you can use notepad to create an empty file with the same name as the data folder and save it as an enl file in the same place as the data folder (library name.enl). You can now open the file with EndNotes File → Open and EndNote should now re-establish your library given that the data folder was unharmed.
See details here:
http://endnote.com/support/faqs/Database/faq8.asp
Best wishes
Jan Ove