Is that video embedded in a web page? If so, are you using IE to view the page?
If so, it sounds like you haven't got the QuickTime Active X control installed yet for your IE.
Go to the following page in IE 9. (It has embedded quicktime movies, and should provoke IE to ask you about the Active X control.)
Down the bottom of the screen you should see a box saying that something wants to run or be installed. (It's been a while since I've seen the box in IE 9 on my system so I can't recall the precise wording.) Click the option that let's the thing run or be installed. Does the video play now?