I was playing TWEWY on my r4 and put it on sleep mode. After I opened it back up the screen went black. So, I turned my DS off and turned it back on. It said that it couldn't find _DS_Menu.dat. I went on my computer and checked my Micro SD. All my files were gone, so I tried to put something in and it said it was full, but there were no files inside.
(It was a 2GB Sandisk)