Activate Windows Server Core using CMD or PowerShell

slmgr.vbs -ipk <WINDOWS_SERIAL_NUMBER>
slmgr.vbs -ato

$computer = gc env:computername
$key = "AAAAA-BBBBB-CCCCC-DDDDD-EEEEE"
$service = Get-WmiObject -Query "select * from SoftwareLicensingService" -ComputerName $computer
$service.InstallProductKey($key)
$service.RefreshLicenseStatus()