Visual with No Audio; Win Media

I just got a laptop complete with Vista!(yay...)

Anytime I open windows Media, to play video's of ANY file type (mainly
..avi/mpeg currently are the ones I'm using) I get the visual of the video no
problem, however there is no sound. Sound works on all .mp3s and whatnot, so
it's not my sound.

There are NO error messages that pop up.
However, there is a small red x in the playlist area when the video is
playing.
This is my default player, I have done all my upgrades for everything.

Weird thing? This worked on my mom's laptop, on XP, it plays the video
audio/visual and all.


PLEASE HELP!
--
-Jess