Cannot finalize my movie on OS Mountain Lion (10.8) DP3, always bug !

So ****** off because 'm going to have to do many movie projects for school and nothing seems to be working, every time I try to publish or finalize my project it finalizes, but my video, when i watch it, is only the first 2 seconds, after that the time goes on but there's nothing moving.

I REALLY need help, please find something for me 🙂 !