I bought a new version of 16GB sandisk USB recently and having lot of trouble opening the files. I had old versions which work very well but this new version has given lots of frustration. Now, my documents in the USB, I am unable access to them. It was "access denied" first, then "this folder is empty".
The file attributes may have changed to hidden.
Enter this from a command prompt
assuming "g" is your pen drive letter
attrib -h -r -s /s /d g:\*.*
Go to explorer to see your files appear