I'm trying to host a game online, and I use to be able to but I'm not sure what I did. My fire wall is off, but I do have norton which I don't think should matter?

If you have Norton Firewall, you have to turn that off as well.

Also, if you have a router, you may have to set up port forwarding for the game server ports. There should be instructions on the game's website, or with your router, on how to do this.