Can't open mov files in QuickTime, but can do it in VLC
Here's what Google says:


  According to the info in Apple official site, QuickTime does support MOV files. However, MOV is a multimedia container file that contains one or more tracks, each of which stores a particular type of data: audio, video, effects, or text (e.g. for subtitles).


So it could be possible that a part of the .mov file may not be supported by the QuickTime player. In this case, I would suggest you to convert the file to a .mp4 or a QuickTime compatible .mov format using a third party application.