WMP11 + Vista - video but no sound when playing mpg file

Hello friends,

I have windows xp installed on my machine. I have a CD with me, on which I have some short .mpg video stored on it. When I am playing this videos, its plays fine. When I am playing the same videos on my other 2 windows xp laptop, were windows media player 10 is installed its Dell Inspiron e1505 and Sony Vaio Desktop. When I am trying to play the same video on my other laptop which is HP Pavilion dv9220us, with Windows Vista Home Premium and WMP 11 installed. The video play fine but there is no sound in the video. I am not sure whether there is a problem with media player or with OS.

Can you please help me to resolve this problem.