why is my product key not working let me download but want let me actavite

Hi,

What does it say in detail? Please let me know the error message.

I also need to confirm what product you want to download and which site you visited to download the software.

If it's an Office product and you want to download the installation, based on the description, it could be that your product key is not valid, probably it has been used before. Then I suggest you contact the customer service to ask for further assistance in this case:

http://support.microsoft.com/gp/customer-service-phone-numbers/en-us

Regards,

Melon Chen
TechNet Community Su