I have a Toshiba Satellite and the sound quit working after a Windows Update a few months ago. I rolled back the audio driver to the previous rev and it started working again.
At the top of balance boxes, in volume control, under microphone, phone line, and PC speaker, the slide arrow doesn't have the green at the top and bottom of the arrow. The computer is 8 years old and probably needs taking apart and cleaning, but I'm afraid that the sound card built into the mother board is toast.