For some reason, if you forget to activate the Remote desktop, and the Datacenter is far away, you can easily activate this feature, by doing the following steps.
First you login in one computer or server, in the same domain.
Open Registry, and connect to Network Registry.
Change the REG_DWORD fDenyTSConnections, from 1 to 0.
Now you can connect to your server, as Administrator.
If for some reason, don´t work after changes, please reboot the server. Open a command prompt and write the following:
shutdown /r /m \\SERVERNAME /f /t 00