Recently, I've lost all my photos from my SD card. I put my SD card into my laptop and windows explorer couldn't find any image.
I did googling and found very nice free PC inspector Smart Recovery. Search on google and downlaod your free copy.
It recovered 500+ images from my SD card.
So next you find your USB stick or SB card is corrupted and could not find the data, try this free tool and hopefully you may get all your data back.