Well, it happened to me before but I did not know why. I pressed the "Yes" button when there was a pop-up screen asking me to "Scan and fix", then I found all precious photos and video clips on my SD card were gone. I googled my problem trying to find out some way to get them back. There were many programs suggested on the search result and I chose one, the Jihosoft Photo Recovery. Seemed this tool served me well. Maybe you can give it a try!