How to connect Macbook to Windows in the wireless mode?
GotToMyPC is much like LogMeIn, Teamviewer and other similar apps, they require communication back to the company's servers so they can contact the app installed on the other computer. Don't get me wrong they are great and helpful utilities but if all you are trying to do is screen share between Mac and PC (without a third party in the middle) there is a way.

The Mac does not use Microsoft's RDP protocol, rather it uses VNC. Yes Apple Remote Desktop is based on VNC. If you turn on screen sharing on your Mac and get a VNC program for your PC you should be able to connect to the Mac from your PC as long as both are on the same network.