I've been playing fine since last night, but when the server just went down and the realm list came up, I accidently clicked on one of the dev test realms. Now whenever I try to connect it just instantly disconnects without even showing me the realmlist.
SOLUTION: Change your realm list to another private server & make an account there. Log in to one of their realms. Logout and change your realm list back. Big thanks to Simon who posted this solution on another thread.