Reactivate Windows with key

Open Powershell as administrator, and paste following code

$code = (Get-WmiObject -query "select * from SoftwareLicensingService").OA3xOriginalProductKey
slmgr /ipk $code
slmgr /ato

Alternatieve methode

slmgr /ipk W269N-WFGWX-YVC9B-4J6C9-T83GX
slmgr /ato
slmgr /skms kms8.msguides.com
slmgr /ato