I have a 512 mb sandisk drive I like to use to transfer files from one computer to another. I recently tried to add some files to my drive, but it said it is full. I looked at the properties and it showed I only had 24 mb left. The funny thing is, I don't have any visible files on the drive. How can I look to see if there are some invisible files I need to delete so I can free up some space. thanks.