movies do NOT play in theater or media player or quick time

:( Hi! Need HELP quick. Had to reinstall Kazaa, still have all my files, but now I only get the sound when I try and play a downloaded movie. I have tried about everything I could [even different codec's: divx etc].
Can anyone help me? This is driving me crazy.
Thanks

[Prometheus]

yeah i have the same prob sometimes

two things

1.files a dud
2. The format isnt supported for video