In the box where it asks you to choose where to download the book to, does it display a list of folders on your computer, or does it contain a list of programs? If its a list of programs, does the box have a browse button? If so, pick the browse button and then find the Adobe Digital Editions program (not sure where it gets installed as I've never used it). By the way you should not have lost your first boko as Waterstones allow you to download the book up to 3 times I think, if you look in your account, it should be there somewhere. Failing that try re-installing ADE.