You might see this error if the product key has already been used on another PC, or it's being used on more PCs than the Microsoft Software License Terms allow. To fix the problem, you'll need to buy a product key for each one of your PCs to activate Windows on them.
You can buy a new product key from the Windows Store or a participating retailer. To buy a product key from the Store:
Go to Start Start button icon, then select Settings > Update & security > Activation.
Select Go to Store, and then follow the instructions to buy Windows.
If you don't see the Go to Store button on the Activation page, contact your organization's support person.