are you sure don't have any sort of firewall turn on, on your pc?
have you done all the windows updates? -i know it sounds stupid, but it really does help in a lot of cases.
are you sure the key is correct? making sure theres no extra spaces before or after the key, or that your username and password is correct with proper capitalization.
I've run all the windows updates I have to run, still not getting the authentication. Re-written the password in every fashion or form. Caps, No caps, etc.