The Gateway website should have the audio drivers for the original motherboard but you said in the original post that you had replaced it so you would need to find the manufacturer of the new motherboard and go from there
I believe the new motherboard is the same manufacturer. The computer boots up with the Gateway logo first thing. The sound driver from the Gateway site is for Windows XP. I have Windows Vista on this machine. I have downloaded this driver and followed the instructions, but it does nothing. Anymore ideas?