Unable to open PDF ebooks

I can't open any .acsm books, only epub books.

I've tried downloading the new Adobe Digital Editions (4.5.7) for Windows, uninstalled it, reinstalled it, restarted computer. Any PDF ebook (.ACSM) I download from my local county library or the from sample Adobe library and it says "Unable to open".

The computer is authorized.

I then tried uninstalling the 4.5.7 version and installing the 3.0 version and opening the books but Adobe Digital Editions says "Error. Check Activation"

The computer is already authorized and I can't unauthorize it no mater what I try.

Any help?