Has you try:
Start Digital Edition.
Go to file > add to library.
Choose the file.
When I try add library The document you want add already exists in the library.
Then seems your Library damages.
Closed Digital Edition.
Go to My Documents and rename the my digitaled Folder to My digital Edition.old
Then start Digital Edition again and try to open the eBook
Now I do have downloaded ebooks showing up in My Digital Editions. However, none of the actions (File, Library , help) are responding. And each ebook downloaded has a "cloud with a blue check" in the left upper corner. I have not renamed the digital folder to My digital Edition.old yet. Still need help. Thanks.
You should rename that the system create a new library.