You have done everything correctly as far as I can tell in your instructions. Did you make sure that you have checked the option for allowing connections from computers running any version of Remote Desktop (less secure). The version of RDP included on the phone and that is floating around here is based on older tech so your Windows 7 box needs to accomodate that. Make sure that you have set up the port forwarding on your router as well and enabled it
hope this helps!