Looks like this system came with Vista, did you install Win 7 on it? You can try the Vista drivers for the audio, if that does not work, either go back to Vista or live with no sound. I'm assuming you installed Win 7 on this yourself, you need to check system compatabily before installing anything.
As jimmy22 pointed out "not working properly" is not a good way to describe an issue. Is it not working at all? Is it playing random music you don't like? Did it steal your wallet?