I'm not an expert in this, but when you start the client, the first thing it does is say "am I up to date?" To find this out it asks a server. If there's a problem with the server itself, or with your ability to connect to the server, then the client can't actually get an answer to that question, and rather than risk allowing you to try to connect with an outdated version (which could cause a slew of problems) it simply says "nope, not doing anything until I get that answer". It -might- be related to the current hub issues plaguing XIV, GW2, and several other games.

On a related note, several posters with similar issues say that doing a clean install worked for them, so if all else fails you could try to redownload.