Today there has been problems with a lot of people not being able to log in to WoW.
Right after they enter there user name and password and then click Okay, they get disconnected.
Blizzard is aware of the problem and is working on it.....
BUT there is something you could try:- Open the Command Prompt (Start --> Accessories --> Command Prompt)
- Type "ipconfig /flushdns" without the "
That's it....Start WoW and log in