<human>: Can you give me a shortened version of the text?

Hey /r/askreddit, I have a question for those of you that are more experienced than I in this realm of computer prowess. 

I'm trying to create a Garry's Mod "Listen Server" (Lingo from the wiki) by clicking on a map and selecting play multiplayer. 
   Right of the bat that didn't work.

So I read online that you need to forward ports, so I did [Pic]  That didn't help either, as my friends whom have stuck with me through my blunderings still got a "Server Not Responding" message.

So I made a DMZ, and forwarded every port to my laptop. [Pic] That didn't work either.

So I called my ISP to see if they block any ports. They Don't.

So my question is this: Is there anything I could have missed?

Any help is appreciated! 

Thank You!

Some more background info: 

I'm running a Mac on 10.6, but that *shouldnt* change anything. 
I'm logged into steam so that's not an issue.
Everything is up to date.
<bot>: Garry's mod make your own server function isn't working... Forwarded ports, made a DMZ. Yet nothing.