There are several reasons why a product key might not be accepted:
·The product key you typed doesn't match the key assigned to Windows on your computer.
·Microsoft has identified the product key you entered as counterfeit.
·The product key has already been used on another computer.
First, check your product key and retype it. If you're sure that you typed it correctly and your product key is still not valid, you will need to buy a new product key. To get genuine
Windows, go to the genuine Windows website and check to see if
Windows on your computer is genuine. If it's not, follow the instructions to buy a new product key. (http://www.microsoft.com/genuine/)