My server always appears dead

[Yo Face]

I know I'm a noob, but whenever I host my own internet server, it appears dead on the server list. My friend tried it with a different computer to make sure it was dead, and it was. Plz halp.

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[Yo Face]

Oh, and I have a Mac in case you're wondering

[Badspot]

http://forum.blockland.us/index.php?topic=40783.0