Folders & Files Have Suddenly Disappeared

I'm using several internal hard drives with my computer, one of which is 1.5Tb in size (on a single partition). On this HD I store a number of multi-media files, which I've sorted/placed in specific "main" folders (Audio files - Picture files - Video files - etc.), and within each of these main folders are a number of other folders where the contents (pictures, etc), are sorted/filed for easier access.This evening I noticed that all the files (several years of pictures), which were within a main folder labeled "Pictures", have disappeared (they were there a few hours before)!! T he main folder was still there, but now shows as being empty, but all the sub-folders and their contents have suddenly disappeared. Everything else on the hard drive is still where it should be.I checked the main recycle bin on C drive, but the files weren't there (there was one photo there which I deleted yesterday. I did a "restore" for it and it left the recycle bin but didn't show up where it came from - the HD where the other pictures have gone missing from - or, as far as I can see, anywhere else).

I also checked the recycle bin on the actual hard drive where this mystery occurred and discovered one "folder" containing almost 5Gb of something - - I can't open it. A check in properties shows this folder to be marked as "hidden" and the box is shaded out, i.e., blocked to prevent being changed. The box immediately above the hidden box (Read-only), isn't checked - but, instead of being blank, it's blue (and if I click it the blue is replaced by a blank box)!!I've read in this forum of some similar experiences - but usually they're program files on C drive that have disappeared and not actual "stored" files on another HD, so I wasn't able to receive any help from them - - except to be comforted in the strong possibility that the files are still there, they've just been hidden by windows (7 Ultimate, 64bit).I also contacted a company (BitMart) who's product (Restorer 2000 Pro), I purchased several years ago. I'm told that my product does not support either W-7 or 64 bit but their newest version does - - however, there's no guarantee that a recovery can be made if the files haven't been deleted from the drive and are only in a hidden state.