I have been using this device for a very long time and have many files stored on it that havent been backed up.
When I plug it into the usb port on my computer I get a pop up message "You need to formate the disk in drive F: before you can use it. I’ve tried using it on several other computers and I get the same message.
If the files are important you might try a professional service. I think SanDisk has a link to one on their webpage. If the files aren’t important you can try formating it. And if that doesn’t work.you might still qualify for a free replacement drive.