sorry for the delay in getting back to you. do you know what the tech at the store changed?
as for the sound, it is likely jumpers on the motherboard. it is common these days for their to be some jumpers that can be used to pass the sound to the rear jacks. these have likely been removed accidentally.
if you have the book for your mobo, it should be stated pretty clearly where these jumpers are, and the correct setting to get things working normally.
if you dont, say so, I will see if I can find the info and point you in the right direction.