For some reason Windows Media, Windows Movie Maker and Winamp all crash when i try and play a video. But if i open it in quicktime it plays fine.

I tried creating a little movie the other day on movie maker, i dragged the clip into the window, it appeared and when i began to play it the movie started then 2 or 3 seconds later it hanged... then tried ending program but couldnt get task manager up so had to turn computer off and on. Its the same with the internet, if i click on a clip to preview it before i download it, mt computer just hangs and i have to turn it off and on again.

Any ideas?