Where is the sound?

[Elizabeth42]

I've been trying to figure out DivX and what software I need to install, and am still having problems viewing some avi videos. When I try to watch some videos on Windows Media Player, a codec is installed however it does not work and I get picture but no sound. The Playa does not work any better, and I have installed codec 3.11, 4.11, and something called DX8INT however none of this seems to help. Any ideas on why I'm not getting any sound, or what I can do to fix this?
Elizabeth