Well not sure, but i have also phone with by cabel provider only i also use a router ot forward a port and for my other server. In that router i use portforwarding and everything works fine. maybe it is your dmz server in your modem/router, put it off or check if your firewall doesn ' t fuck around with your connection. Also do not forget to use the right internal IP, because i know people that know exactly waht they are doing but from one moment nothing works anymore, and they forget to see if the ip has been changed.
Good luck, this is all i can say..........
