My Compaq Presario C500 C551NR won't play any sounds through the internal or plugged-in speakers. Please Help!

My Compaq Presario C500 C551NR notebook won't play any sounds through headphones, or the internal or plugged-in speakers. This started a few days ago, and I have tried doing a system restore (failed several times) installing a new sound driver, and plugging in different external speakers. It will not play music on iTunes, anything streaming from the internet, or any of the regular beeps and boops that normally come from a computer. iTunes seems to think it's playing, since the little slide below the song title moves, meaning the song is playing, when I click on it. Also, the little synthesizer that appears when you click on the volume on at the bottom of the computer screen moves to the beat of the song (if it were audible) so the computer think it's playing music. The volume bar says SPDIF Interface, Conexant High Definition Audio, if that means anything to you.