Here is some tips it may help you.

1- Go to your router in NAT area and open the port for remote access. i am not sure what exactly parameters is in your router. But you can do the similar.

Port : 5900 and put the IP address of your PC where VNC is installed.

2- Install teamviewer http://www.teamviewer.com/download/index.aspx
This is more easy with no configuration in router side.

Good Luck