Nostalrius Begins - Quality wow vanilla realm (1.12)

Hi, when I try to log in it takes me to nostalrius begins Pvp realm. However, the message "logging into game server" is shown and it fails to do so and then it gives me the realm list to choose a different server but it does not allow me to join any of them, why is this?

If you're continuously shown the realm list, that usually means the server's in the process or restarting or is down from a crash or something. Wait like 30 minutes and try logging in again to see if it lets you in.