Since the Repair Tool has been removed with patch 5.0.4 I wondered how can I repair the game.
I wrote to a GM on the EU realms and this is the answer I got from him:
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"Shut the game completely down if it's not already.
Delete the Cache folder found within the World of Warcraft directory.
Delete the WoW.mfil, WoW.tfil, and WoW.pfil files found within the World of Warcraft folder.
Delete the Battle.net folder - http://us.battle.net/support/en/article/deleting-the-battlenet-cache-folder-pc
Start up the game (run WoW Launcher.exe) and Agent will redownload all of the missing data, hopefully without any corruption this time."
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I hope it will be helpful if somebody would have to repair the game client.
It helped me when I had an issue with the same loading screen everywhere in every zone.

Thanks for sharing, stickied