If you are trying to log in to Cata classic on any OCE realm then it seems the servers are currently unavailable.
Common behaviour seems to be is will say “connecting”, then “retrieving realm list”, then “logging into game server” then crashing out without reaching character selection. A few people report actually seeing the a server list showing all three servers offline before getting crashed out. But the problem appears to be the servers being unavailable combined with no opportunity being given to try and switch to a non-oceanic realm list