Problem with playing movies and clips in Vista

A couple of days ago, I upgraded to windows vista. But now I want to play all my movies in Vista but with some movies and clips the only thing I have is audio, no video.

I tried to play my movies and clips in windows mediaplayer, bs player and vlc player. All the same.

What is the problem? has it to do with vista? codecs? player?

For example: a .avi file plays only audi, no video