MightyOhm.com

Sounds like a problem with your home network. It almost feels like your ISP is blocking the router, like when you don't have NAT set up and try to use more than one machine on a cable modem... I don't know the answer, but maybe if you describe your home network a little bit (what router you are using, any unusual settings, etc.) I can try to help. I am not an expert on this, usually it "just works" for me.

You can put the mp3 in any directory you want, but I would put it in /root. Then execute "mpc add /root/file.mp3" and "mpc play", the file should play.

Not that I know what your issue is, but adding a port to a ping command doesn't do anything. Ports are a TCP-level thing, and Ping does not work at the TCP level.

Can you wget a regular website page from an external site? What about:
If that works, but the mp3 file doesn't, then something fishy may be going on at your ISP's side. If getting a regular page doesn't work eather, my bet would be on a local network or firewall problem. How is your router connected to the internet? Are you using a Lan port, the Wan port, or wi-fi?

Jeroen