ADE worked once after new install, but blank thereafter

I'm transferring to a new laptop. I installed latest ADE from website, authorised the new PC, and it opened with all the books I had on my old PC. Checked it was all working by opening the "Welcome..." book. Great. job done, or so I thought. Closed ADE down, went on to do something else, and re-opened ADE later. Now it's totally blank (see screenshot). No books, not even the "Welcome ..." one I looked at earlier. Most of the menu options are greyed out as well. Have tried closing and re-opening several times. Also tried adding the "Welcome" document to the library (that's one of the few menu options not greyed out) but it tells me it can't do that because that book is already present in my library ... but I can't see it! Any ideas what's gone wrong here? Why would it open properly once but not thereafter? Thanks in advance.