A. Sometimes installations can get a little confused about their product keys, especially when you've been given a Sysprep'd image you duplicate. So the easiest way to activate via the KMS is to re-enter the KMS key for your version of Windows—they're listed at on this TechNet page—then activate. Below is an example for Windows Server 2008 R2 Enterprise edition.

C:\Windows\System32>cscript slmgr.vbs /ipk 489J6-VHDMP-X63PK-3K798-CPX3Y
Microsoft (R) Windows Script Host Version 5.8
Copyright (C) Microsoft Corporation. All rights reserved.

Installed product key 489J6-VHDMP-X63PK-3K798-CPX3Y successfully.


C:\Windows\System32>cscript slmgr.vbs /ato
Microsoft (R) Windows Script Host Version 5.8
Copyright (C) Microsoft Corporation. All rights reserved.

Activating Windows Server(R), ServerEnterprise edition (620e2b3d-09e7-42fd-802a-17a13652fe7a) ...
Product activated successfully.

I just keep the two lines in a bat file, so I can run

cscript c:\windows\system32\slmgr.vbs /ipk 489J6-VHDMP-X63PK-3K798-CPX3Y
cscript c:\windows\system32\slmgr.vbs /ato