I found the problem, no thanks to Adobe tech support. I read in one of your other posts about the file 'manifest.xml', so I opened it in a text editor to look at the contents. I found all my books, and started commenting them out one-by-one, until I found the one that was causing the problem. After I deleted it from the XML file, ADE opened without problem.
In my opinion, this is a bug in ADE. It shouldn't hang just because there's some invalid document in your library. It should display an error message, skip the invalid document and continue. This is User Interfaces 101 stuff. I happen to be a computer programmer so I'm familiar with XML syntax, but otherwise I would have been stuck. (The tech support agent suggested the problem might be related to the firewall on my computer, etc. None of his suggestions were really relevant to the problem.) They surely don't expect all their users to be familiar with XML, do they?