There are many reasons which files and folders are hidden. So you need to find out the reason and then try the solution.
The most common possibility is that files or folders property is set to be hidden. You may show hidden files and folder first, then you can see them.http://goo.gl/4IucVW
Another possibility is that files and folder could be lost. You may try to recover them with some memory card data recovery software, you can see this step by step tutorialhttp://goo.gl/HBtYb
It also could be possible that memory card is infected by virus. So you may have to scan the memory card with anti virus softwarehttp://mayshare.is3.revenuewire.net/stopzillaav/download