Whenever someone tries to connect, it says server not responding.
When this happens it's because the host didn't have the right port open.
Search for "port forwarding" on google. Knowing the model of your router might help.
A quick solution is to enable DMZ for the hosting computer.
If everything fails or seems way too complicated you may use a LAN simulator program like Hamachi or Tunngle.
Just to be safe: if you have a firewall installed make sure it is not blocking the game.