I’m presuming that you are using something other than windows xp. I would recommend that you download RDCLI.EXE from microsoft’s website and use it. Here’s a link:
Your d-link router must be pointed to the computer on your internal network, that port 3389 is opened for.
In other words, you cannot open port 3389 without specifying the ip address of the “internal network” destination.
Also ensure, by viewing the target computer’s power options, that hibernate is not enabled, as this will allow the computer to shut itself down and consequently will not be available for a network connection.