Hi there and welcome
To authenticate,Press the windows key + X and click on Command Prompt (Admin).
Type slui 3 (note there is a space between slui and 3) in the Command Prompt window and hit Enter. Type the product key given to you when you downloaded Windows 8from the software site.
It will then be authenticated
If you have any problems, or would like any additional information or assistance, please do not hesitate to let me know.
Else if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.