Windows Server 2012 Activation using CMD:

Open CMD as administrator:

> Slmgr.vbs –ipk your product key
> Slmgr.vns –ato

To “rearm” Windows on the any demo virtual machine after the expiration:

> slmgr -rearm
Restart
> Slmgr.vns –ato

To open the activation screen:

> SLUI 3