problem statring server

[vistavsxp]

couldn't allocate dedicated server udp port
i know many people say remove ip, when i remove then i have lan server but i need internet server.
i have port 27015 and this error couldn't allocate dedicated server udp port modem i dont know how to forword and i havent router i have just dsl/cable i was trying to write more diferent ports or turn firewall off but still get this shity error.
maybe i need to just forget to make own server HELP PLZ

[Dub]

ur cable modem has a weite u can go to as well. since u said u tunrned off ur firewall and u still get that then we know ur firewalls not the problem. but yea i m not sure if ull be able to configure the settings in the cable modem. but call ur Internet provider and u can ask them to help u out with it.