Did you try turning off Key Maps (Shift+Alt+M) in order to enter your password? ...

http://isboxer.com/wiki/WoW:Quicker_...Part_2:_Log_in
Don't skip this part. If you skip this part, you are going to ask me why your password doesn't work. It's not going to work because Key Maps are enabled and you don't want your keys to be mangled when you're entering your password. You want to type in your password, not activate auto-assisting.

So, turn off Key Maps to enter your password. To do this, use the Shift+Alt+M hotkey, or click on the "A,Z" icon that starts out with green (activated) arrows.

If your password is the same on all accounts, you can enter your password in all windows at the same time via Key broadcasting. To do this, use the Shift+Alt+R hotkey, or click on the "A,A" icon that starts out with gray (deactivated) arrows.