Videos have header files associated with your movie which serve like a road map in terms of giving instructions to your computer. This header file has all kinds of technical information which not being present, will prevent your computer from even opening the file (let alone playing it).
Recently I had a problem when one of my video header files became corrupt due to a power failure during filming. Given the header file is the last item written to a video file, if power is ever interrupted to your camera, you will have a major wasted effort. Editing a header file is not for the weak of heart, and even this "nerd" did not want to make the attempt.
After hours of scouring the web for some means of rescuing my video, I found a great (and free) utility named Fix Player (review and download options via Softperdia). This software package saved me from disaster. I was able to open my corrupt file, view it, and most importantly … save it successfully with a new header file (use a new file name).