Welcome to Android Central! Are the stored on the microSD card or Internal Storage? If the former, then the card is probably corrupt or failing. Unmount it immediately (in Settings>Storage), remove it, and insert it into your computer. If the computer can read the files, back them up now, before they all get lost. Then run chkdsk to find bad sectors. http://forums.androidcentral.com/am...guide-using-chkdsk-fix-corrupted-sd-card.html