How to see hidden files hard disk or flash

Hello,
I have so many movies, files, folders & musics in my external hard disk . Due to some virus or something I don't know when I opened the external hard disk I can't see some folders inside it, but if I wrote at the top at the search bar the folder name or the movie name which are in inside the hard disk I can find the folder . So please if you can tell me what is the problem .