Some ISP's or firewalls may block the default port 3389, and changing the port may be a successful workaround.
Basic Summary Below:
Go to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\TerminalServer\WinStations\RDP-Tcp\PortNumber
Modify the decimal value of the portnumber and reboot the computer.
When connecting to this computer with a different port number you will need to manually specify the port. If you are going through a SSL tunnel instead of localhost:3389 you would use localhost:portnumber. If connecting using Remote Desktop directly you would connect as yourhomeip:portnumber. (http://support.microsoft.com/kb/304304/)