Usually you can't join the server via your public IP when it is hosted on the same machine. Ask your friends to join it. You should join your server using the LAN tab.
Could you please provide more information from the logs? Does it say an error or something suspicious while you join the server? Often, having this problem is dealt with wrongly set firewall settings. If you're using a router then check if it possesses a built-in firewall or not.
In this case, you must change your firewall settings in order to connect to your own server (and Windows Firewall as well). This should fix this up in most cases. Otherwise, do what VADemon mentioned in his post.