Sometimes you are admin and have access to a remote machine by Windows Explorer etc but you need RDP to be enabled.

For that you need to connect with regedit.exe remotly to the other machine (maybe the Remote Registry is not running and you need to run it manually) and change a value within the registry:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server] "fDenyTSConnections"=dword:00000000

With that key you Enable Remote Desktop connections (by default is has 1 as value and you need to set it to 0)

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp] "UserAuthentication"=dword:00000001

With that key you Enable Network Level Authentication (normally it is already set to 1)