Server Problem: Server does not appear in Steam Master Server list

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=165

Usually this is caused by one of several things:

1. You don't have both TCP and UDP forwarded for your server port (27015 typically).
2. Your uplink was congested when you started the server.
3. You used the "map" command more than once when you started the server. You can only use one instance of "map"; after that all other map changes must be invoked by the "changelevel" command.
4. Check to see if you have two NICs (network cards) in your system, you might want to try disabling the one that isn't your active Internet connection. You might need to flush the routing table after doing this, then start your server and see if the problem is resolved.
5. Also try adding your external IP address in the Server launch properties (-IP <your external IP address>).