Vista - WMP plays video avi but no sound

We recently gave our kids a Samsung 730 digital camera. We recorded some
video today and when I play them back on the camera the sound is fine. When
I uploaded the video to my Dell Dimension DXP061 running Vista Home Premium,
WMP plays the video fine but there is no sound.

All of my MP3 files play sound fine but the AVI files don't. I loaded Gspot
onto my system to confirm that I had the right codecs to play the audio
portion and it suggested that I did.

I have not loaded any other media players on my system and in fact
uninstalled some of the ones that shipped with the machine originally as they
seemed to be having challenges running on Vista. So I am not sure if the
AVIs will work in other media players. I will email them to my office
machine to try but I thought I should get a post out there to see if there
was something specific to Vista.

Thanks in advance for any help that you can provide.