First Restart to get rid of any errant Blizzard programs like Launcher , Agent , Background downloader etc etc
Then delete these folders :
* Cache folder in World of Warcraft folder
* Cache folder in the Data folder inside the World of Warcraft folder
Then open this folder :
Wow folder -> WTF -> Account -> Your_account_name -> your_realm_name -> main_toon_name
and delete the cache.md5 file.
Then open from the Launcher.