My Ultimaker 2 randomly started not showing any files on the sd card about a week ago. It didn't come up with the no files message, just didn't have anything listed. I pressed the button and it showed a file name and said it was printing it but didn't heat up the nozzle or bed beforehand. Over the past week I've managed to deal with the problem by simply emptying my sd card and reloading the files onto it and it seemed to work fine, except when I tried to load a new file onto the sd card. Then the whole problem would start again. I tried it with 5 different sd cards, I reformatted all of them but it didn't solve the problem. Now however, it won't show any files, no matter how many times I empty the sd card.
I rely on my printer for my business. I teach children how to use and design for 3D printers, it doesn't have the same appeal to the kids when the can't actually use the 3D printer. Please help!