Game server on internet, fail??

I have cable and we just bought a new computer, we have a router sitting in the internet connection to share it between the 2 computers. We tried to set up a game server, Counter strike 1.6, you may call it Steam. But we had this surprise that no one could come to visit the server because it won't let anyone enter. We thought it were the firewall's, i checked the windows and the router firewalls, but they were off. Do some of you know a solution out of this problem,

Thanks.