Hmmm... tricky one...
Here's a couple of things to try...
1) Run the movie in your browser and right click, check it says Flash Player version 5 -> if ti says 4 thats probably your problem.
2) Have a look at your publish settings and check you are publishing as Flash version 5 and check things like the background colour, etc...
3) When running the movie in a browser right click and hit play to see if there is a stop action or something similar in the first frame...
4) Try publishing both the movie and the relevant html (check the html flag in the publish settings) and then run the html page in your browser; see if it's something in your html code.
5) Run around shouting, "Ahhhhhhhh" and then jump up and down; not highly constructive but it helps to pass the time.
If none of these work / you've already tried them / etc; pop another post on and if I can't think of anything else, someone else will!
=)
PetitPal.