Adobe Digital editions won't load book

I use my Samsung tablet as an ereader. I was reading a book on there, and needed to use my emails, so came out of ADE to go into emails. When I went back, ADE opened, and showed all the loaded books. But when I tried to open the one I was reading, it just gave me a blank page. This now happens on all the books. How do I get into my books.

Also, how do I download the books on my PC ADE to my tablet?