Just to add, I may very well be speaking out of my попа here. I dont know how the Login server is set up, or how WoW works technically, just spewing out ideas. If you get instantly disconnected, my first thought is, it's got to do with either being blocked, or somehow IP related, the login server refusing the IP. 
 
	Again, I dont know the technical details of WoW nor the login server, so I may very well be wrong.
 
	Did you install any network related utilites in the past 2-3 days that may affect your connection?