What do you mean by "just won't work"?
Assuming you mean the server is not reachable, this will vary with various factors. Being behind 2 routers for example will cause issues. Not opening ports on the Amazon's console would be another reason for the server being unreachable. Windows firewall blocking access would be yet another. In the windows OS in particular when you launch the app it gives you a dialog that prevents or allows certain forms of traffic. You will need to provide a lot more information than "just won't work" if I am to help you determine the problem.
