If you can not connect since the last maintenance, read this.
Hello Citizens of Dalaran,
After the latest changes some players may experience difficulties to log in. If this is your case, just go to your World of Warcraft folder, then enter into the WTF folder and delete the file named: "Config.wtf".
Now, you should be fine and able to log in again.
Thank you very much and sorry for the inconveniences.