no audio... sort of?

This started happening about a year ago but I never really started to care til' now. It's minor, but meh, still irritating.

All of the sound effects work fine, so does the background noise.
However, music and dialogue (in mission cinematics) is nonexistent (and yes, I've checked my sliders)

Any ideas why?
I'm on vista btw...

Try enabling/disabling EAX/3D hardware sounds.