You must have an account with Mojang. If mc.livingcomputers.org does not respond from a browser, then the server is DOWN.
A map is available at mc.livingcomputers.org:8123/
This will be your opening screen when you start Minecraft on your computer:
Choose Direct Connect
That should get you to our Castle at Python World
If you will often be using this server, or if you use multiple servers, you may wish to add livingcomputers to your server list
For Server Name, you may wish to be more descriptive
Your Multiplayer Opening Screen should now show