The USB might be corrupted, but if you know it hasn't been encrypted with an application, then enable to view all files on the USB. Open Computer and go to View > Options then switch to View tab and enable the Show hidden system files and folders option. Go back to the USB drive and open it. Instead of double click, use right click and select Explore. This is recommended to avoid malware infection. If you see the original files hidden, select the bad ones and delete them, then right click the normal files and go to Properties and untick the Hidden option.
In case the USB is encrypted, you will have to use the same application that added the encryption.