While looking through Data Management at all of the .cia files I had installed, I noticed one that was blank, took up zero blocks, and had no banner. Tried to delete it, which it tried to do for about a full minute, before returning with a message that that file could not be deleted. It deleted everything on my big SD card. All my Gateway saves. None of the games I had installed showed up anymore. My theme was gone. All of my eShop purchases were gone. My card still showed that it was almost full, as it was before I tried deleting that blank file. My only option was to format my SD card, and now I get to start over for the third time. Don't delete this file, if you see it under Data Management.