Help! movies are pixelated/unwatchable - is data corrupted?

Hi, I have been trying to figure this out online. Totally stumped.  Took digital movies with camera, played them on computer, everything is fine.  next day- put the card back in the computer to watch again and the movie is all “pixelated”  totally unwatchable.  what did I do?  how could it be fine one day and not working the next?   Does this sound like corrupted data and would recovery software help?  Thanks for any help or ideas anyone has.