Can only access to my server through “localhost”

Question

I am programming a trading-game, that requires multiplayer. I realized, that my client can only access through "localhost" on the pc the server is running on. How do I figure out if the server is online, so I know if is the firewall or something else? If someone already knows the solution I would be even happier.

Thanks!

edit: My operating system is Windows 7.

Update: I managed to connect to my server on the same computer with two Addresses i found through ipconfig. One that my rooter assinged to me and I don't know were the other one comes from. First I tried the one I found through searching "what is my IP" on Google, wich did not work. I still can't connect to the server through other pc's connected to the same router(fritz-box).

    Server:

    ExecutorService executor = Executors.newFixedThreadPool(100);       

    ServerSocket server;        
    try {               
        server = new ServerSocket(5555);    
        System.out.println("Server gestartet");

        while(true){
            Socket client = server.accept();
            executor.execute(new ClientHandler(client));                
        }           

    }catch (Exception e) {
        e.printStackTrace();
    }       
}

    Client:

    try {
            InetAddress addr = InetAddress.getByName("MY IP");                                  
                //Works
                client = new Socket("localhost",Port);
                //Does not work
                client = new Socket(addr,Port);
                //Does not work
                client = new Socket("MY IP",Port);

                System.out.println("Client gestartet");

                //Streams           
                out = client.getOutputStream();
                writer = new PrintWriter(out);

                in = client.getInputStream();
                reader = new BufferedReader(new InputStreamReader(in));
                // ------------------------------------------------         

                String s = null;                    
                while((s=reader.readLine())!=null){
                    render(s);
                }               
            } catch (IOException e) 
            {
            e.printStackTrace();
            }

I left the ClientHandler out, because I am sure there is not the Problem.

Answer 1

If it's a firewall problem you will get a connect timeout. If you get 'connection refused', the server isn't running.

Do not modify your ServerSocket construction as suggested elsewhere here. The way you're doing it is correct.