Sorry to hear you are having trouble.
pressing "Enter Product Key" does nothing.
As odd as it might sound, that activation window uses components of Internet Explorer.
I want you to open up Internet Explorer, go to Internet options, and set everything to 'default' (primarily the 'Security' and 'Advanced' tab).
Click OK and try to see if the 'Enter Product Key' button responds.
Let us know and thanks for the patience and patronage.
Stardock Customer Service Manager