If the PC will be used for more than 90 days without activation and then be registered follow instructions below:
1. Launch a command prompt window with elevated privileges (right-click, run as administrator).
2. Run the following script, using your product key: cscript %windir%\system32\slmgr.vbs -ipk xxxxx-xxxxx- xxxxx- xxxxx- xxxxx
Run the command prompt in administrator mode by using the browser to navigate to your windows \system32 directory, and then right-click the CMD.exe file and select “run as administrator”