As of today many people are still experiencing problems after having downloaded the latest patch.
We are aware of this issue and trying to fix the problem and push the fix as soon as we can.
Meantime there are 3 solution for the problem, ordered by time/download size:
You just need to try one and if it works that is it. If not go to the following method.
1. Try first to get the wow.exe file and the LoginUI.lua
Wow.exe (goes in the client root directory)
LoginUI.lua (goes in the Interface directory)
2. If the method above did not work for yo try get the new Interface download:
There is a README file inside that explains where the files go.
Then launch the game via the Launcher.
3. If the method above did not work try to get our latest Windows client torrent.
and seed if you can, to help everyone out get the download faster.
If you have any further question feel free to reply on this post.
Hope this helps.