Have you ever your USB/Flashdisk error and appear messages that your USB drive need to format before you can use? The messages appear look like this screenshot.
If yes, you can try to open with DiskGenius Software and backup your important files, and then format your USB drive, and after your USB is back to normal, you can move your files again.
You can doing with just install DiskGenius Software click here, after that Expand your USB that error. Then you can copy your files in another directory, with right click and copy file to S selection. And you’re done.
If you still confuse, you can just follow this video tutorial.