Have you ever plugged in a USB drive, only to have it show up as unreadable? While a simple reformat might very likely be a fix, that doesn’t help if you really need to recover the data stored on it. There are programs out there that can help you out of this bind, but many cost money. However, you might look into MiniTool Power Data Recovery Free Edition.
This software is completely free to use at home for noncommercial use. It has a number of features for recovering data from lost/damaged partitions, deleted files and more. You won’t need to be terribly tech-savvy to get it to work, either. Just follow this guide, and you’ll be set.