I started printing a part and decided I wanted to tweak the G-code. I stoped the print removed the SD card and went to reslice the part. When I came back and inserted the SD card the main LCD screen said SD card inserted, but when I tried to retrieve my gcode files it said there was no SD card. I'm not sure what to do since it was working ten minutes ago and doesn't anymore. I can't think of anything that would have changed, causing this problem.