Argh, this happens to me all the time. >.< Three things are either wrong:
1. Its like my stupid glitch, where you have to exit out of the entire game about five times until it finally just connects.
2. Or your timing is horribly off and the servers are temporarily down when you try to go on. This is probably least likely because they haven't been down as often as they used to be, or for as long for that matter.
3. This happens to me when my internet connection is down or when it is very poor. Maybe you should check your internet connection and make sure it is strong enough.
If it is none of these circumstances than it may only be fixed by uninstalling and reinstalling with a new installer. Don't use the same installer if you believe reinstalling it again would work.