Adobe Digital Editions(Win7) looses my ebooks.

Here's what happens:

• Installation of Adne´be Digital Editions 4.0.2 (German)  , Registered witrh my Adonbe ID
• Download an ebook with my Adonbe ID ==> ebook does not appear in ADE.
• Downloaded one of the free ebooks from Adobe == ebook appearesin ADE
• Quit ADE (no error message)
• Restart ADE ==> no kontent at all
• The directory my Digital Editions exists and has the ebools stored.
• When I try to add to Library (CTRL-O) the system says "document already exists in library"

Any idea what goeswrongand how tofix it?

Help is much appreciated

Christian Georg