i have the exact same laptop, with windows xp pro. Sound comes only through headphones, not through speakers anymore. I've had the problem before, but it somehow fixed itself. But now the problem is persistent. I haven't tried linux, but i have tried sound-card-driver-update (with zero result)...
if someone knows how to solve this (without opening the laptop myself) i'd be very gratefull. But i think its something in the cabling, and the only solution is bringing the laptop back...
and yes, i have tried every setting i can find that comes near sound-settings....
it happend like this: i was working on laptop with headphones at my work, and when i unplugged them the sound was gone. No changing of any settings went ahead of this behaviour.