Activating The System
The Windows Server 2008 Core Installation must also be activated through the Internet. To do this, enter the command slmgr.vbs -ato in the console.
Activating the server
If no other message appears, the activation was successful; otherwise, a dialog box with an error message is shown. To ensure that you can see any errors, activation should be done from the remote desktop and not from the remote shell.
Errors in activating