Macbook, SigmaTel High Definition Audio CODE

I don't know why, it works well at first,

then I got no sound , both the internal speak and the 3.5 mm output,

but I can see the red light comes out from the little hole, and the little speak icon on the Windows XP task bar. so it should works in the optical output mode,,How can I change it back?!?!?

thank you ~~