No Sound

Hello, I have a Compaq Presario v6000 laptop. Recently I have done some updates to it like update windows vista. Today i tried to listen to some music, but it wasnt playing anything... so i looked in the bottom right hand corner by the clock. it has a little picture of the musi thing and a red x over it. when i move my mouse over it, it says 'no audio ouptpu device is installed'. I tried puttin in plug in speakers and headphones but still no sound. is there a something that i now need to install, or anything? please help!