After successful installation of your oS 8.1 you will notice that a pop up will come up telling you to activate your windows by putting product code which they might ask you to purchase online.
Your Windows Productkey is buried in the registry, but it can be easily extracted by using a free key retrieval program so you don’t need to start looking for product key online.
How to fully activate windows 8.1
==>Download key retrieval from here
==>Run it then click on recovery; now you should see your product key write it down somewhere or you can copy it to clipboard.
==>Now search windows by pressing window+R then type slui3 there the menu will open just paste the product key then in no time your windows will be fully activated…shalom