I recently needed to login to a computer on a LAN that did not have Remote Desktop enabled. Here are the high-level steps that I took.
If you search online, you will typically find references to a registry setting to enable RDP.
HKLM Hive -> System -> CurrentControlSet -> Control -> Terminal Server > fDenyTSConnections should be changed to zero.
That’s not sufficient in most cases.
You also typically need to allow Remote Desktop through the firewall. I did this using Sysinternals psexec tool to get a command prompt to the remote machine.
i.e. psexec \\remote-computer cmd.exe
Then running a netsh rule to enable RDP:
i.e. netsh firewall set service type = remotedesktop mode = enable
Also, I needed to add the user to the local computer’s Remote Access user’s group (not the exact name).
A reboot was required.
netsh firewall rule: http://technet.microsoft.com/en-us/library/cc736451(v=ws.10).aspx