Authorization of old ebooks

My computer is new and so I had to download Adobe Digital Editions again.  I purchased two ebooks and downloaded them to ADE only to realize my old ebooks weren't there.  Then, I discerned that I wasn't signed in with my AdobeID, yet.  When trying to authorize my computer to get my old ebooks back in with my recently downloaded ones it displayed this message:

I need all my ebooks together on this computer and don't know how to do that if it's not letting me authorize this computer.