vista, Go to start, Click control panel, then choose hardware and sound,Then choose sound,Under playback there should be a green check mark on the Realtek High Definition Audio, and should say working.
Click once on the speaker picture, Now choose the option configure in the bottom left of window pane, then from the options pick quadraphonic, then click next and make sure that the options front left and right and surround speakers are checked, then click next and finish.
find the audio device icon, so what to do is go back to control panel, sound and under the playback tab, it told me that 'no audio devices are installed' and so i 'right click' and select/check 'show disabled devices' and the audio device icon appear and then i just enable it and it work again. so hope that help.