HP Pavilion a6403w with onboard video & sound (MCP73M02H1 motherboard.) Windows Vista. Short story is the video card went out & I replaced it & now the sound don't work. The video went out gradually, monitor would go to sleep while he was playing a game, this kept getting worse until it quit working altogether. The sound worked until I put a vid card (asus en8400gs) in it. The device manager says sound is installed & working properly, but if you try to check the volume/mute it won't come up...says there is no sound device installed.