I am unable to sign into Digital Editions with my Adobe username and password on my Mac. Digital Editions has me logged in as my library card number so I am unable to authorize my computer to download books. When I do download books using the library card account I cannot open them on my Nook. Please help me.
It sound like you want to sign out of ADE and then sign into another account, but it's not letting you?
If that's the case, you can follow the instructions here to get that sorted out:
Make sure you follow the instructions for Mac!