Changing the resolution causes client to go invisible

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Hi,

Every time I try to change the resolution I can no longer see anything but I still hear the music and the menus. The only fix I have found is deleting the entire game folder and using a fresh one, but again I cannot change the terrible resolution. I also tried the resolution trick by opening retail WoW to get the high resolution but this does not work after I hit No on the "reset to default hardware." 

 

How do I fix this invisible client problem?

Thanks for your help.