Can't open any e-books not even the sample one

I have installed Adobe Digital Edition 4 on my PC and am trying to open a e-book,. when I download a book and click to open the message "Fullfuling the "name of the book" pops up. Once the fulfulling is done nothing appears in the Adobe Digital Edition. What am I doing wrong? Restarting the computer and uninstaling and later re-installing the Adobe Digital Ecdition did not help. Thank you