on having the proper driver for your Realtek audio card?
I don't know myself as I don't use Vista, but maybe your audio card needs a driver update.
Okay, now here is something that has been bugging me. When I had XP on my computer, Realtek HD Audio manager looked like this and had a graphic equalizer so I could mess with the sound. But with Vista Realtek HD Audio Manager looks like this and there is no graphics equalizer. I used the same installer under both XP and Vista. Is there any way I can get the graphic equalizer back on Vista?