Something with the files, as written by the camera, as stored by the memory card, as retrieved via some method, or as stored on the computer.
Do the files look a reasonable size or are they truncated, somehow?
How did you transfer the files from the camera to the computer hard-drive? You might try alternate methods of moving the files from camera to computer, to see if you can isolate if it is the cable or the card or the reader or another aspect.
