Remote access to my desktop at home

I am trying to acces my home computer from my office without success.
I have Belkin modem. I have set the Port forwarding IP address to the IP address of the desktop. When I try for example files://nnnn.nnnn.nnnn.nnnn:3389 , it comes back with an error message that it can’t find the address.
Any help on this will be appreciated.