No one can join the server? The server doesn't show up on the master list?

[Spartanfrog]

Things you need to know how to do:
How to find the internal IP of your server
Answer:
Make sure you have forwarded your ports. Goto http://www.portforward.com. Then on the main page click on the Routers hyperlink, then click on your router on the next page. Then find "Steam Server" and follow the directions.

Still doesn't work? Or, already did that?

Next thing to try is to DMZ your router. In basic terms that really means directing all unknown traffic to a designated IP address. In your router homepage, there should be a DMZ option under advanced topics or it may even be under normal router configuration. Just place your internal IP of the server in the IP space, and you are ready to go.
*Note make sure you have a firewall on your server because DMZing pretty much opens the server up to attacks.

Still doesn't work? Or, already did that?

Make sure your firewall (if you have one) has the necessary ports open. Even try turning off the firewall to see if the server can connect without any firewall. If it can, you need a new firewall.

Still doesn't work? Or, already did that?

Other than triple checking your ports, the only other options are:
A. Your router is incompatible with SRCDS
B. Your ISP is blocking the required ports
To check for A., if you are able to, plug the server directly into your modem, cable box, etc., and see if the server can be seen. If it can't, chances are that your ISP is blocking the ports. You could phone your ISP and ask for the ports to be unblocked, but beware, bust ISP's TOS do not allow servers.

Still doesn't work? Or, already did that?

Pray and make a post in the correct section.

[Mooga]

When port forwarding, make sure that each port is only listed ONCE and that the ports are forwarded to the correct Local IP. Forwarding the same port more then once (or to two computers) will cause your router not to be able to forward the ports since it doesn't know where it is supposed to go.