open port 3389 on router.
Q. Does Remote Assistance work through firewalls?
A. Yes, Remote Assistance will work through any firewall when Port 3389 is opened. When using Windows Messenger, dynamic ports are used in the helpers ticket. The helpers computer uses the first available TCP port above 1024. When using the Windows Messenger method, the requestor makes the first attempt to establish a Remote Assistance session using the helpers IP address and port number in the ticket. Reference Q306298 Explanation of the Windows Messenger Reverse Connection Process and Q301529 Supported Connection Scenarios for Remote Assistance for more information.
Remote Assistance can also push through Windows XP Internet Connection Firewall (ICF) without enabling TCP Port numbers.