when I try to open a library book on the Kobo, the cover appears and then the screen goes black and I'm returned to the main menu.
Does this happen with all library books or just one? I encountered a small number of books that did similar things to my Bookeen Opus. One even crashed it completely when I tried to open the book. It seemed to be specific to some books. I never tracked down exactly the issue; just read different books.
Also, you may find ADE 1.7.2 works better. ADE 2.0 has problems with XP, and also with some eReaders, especially with library books.
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
http://helpx.adobe.com/digital-editions/kb/cant-install-digital-editio ns.html
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172