If your system sound is not working are you talking about the "Theme" sounds and the web "clicking sound"? Goto your Control Panel>Display>Theme tab and re-select your theme that you want and see if that fixes the problem, also insted of single clicking on your volume speaker (double click to open the Speaker volume control and make sure that the volumes are up and no check marks are in the Mute area expectly in the Wave.) since your themes run off the .wav audio