Books not loading properly?

Hi everyone,

I am very new to using Digital Editions. I successfully downloaded and installed both DE and some books from my course provider. These worked perfectly on the devices to which I downloaded them. Today however whilst I can see the books in my library and select them, I cannot read the content - but can still see the table of contents in the navigation panel. I don't know whether this is a problem with DE, but I know others on my course are experiencing this difficulty and with exams just a week away, it is causing some stress! Any ideas gratefully received.

Thank you.