There are files that have a hidden attribute for many reasons. It might be the case that you have this attribute on. In order for you to be able to see these data follow these steps
1. On Windows Explorer click Tools and then Folder Options
2. Select the View Tab
3. Under "Hidden Files and Folders" select "Show Hidden Files and Folders"
4. Click OK.
Now check the files on your USB. Do you see them? If yes right click on the files and change the unmark the "hidden" checkbox.
If it doesn't work, please follow the following steps.
Here are some trial version shareware program which may help you. Download and check it if it works.
Pen Drive Data Doctor Recovery:
Thank you :)