Onbord sound not working on pcchips m863g motherbord?

its a rather old machine, amd duron 1.35ghz 778 mb of ram ati RADEON 9225 (except the card everything calls it a 9250) that is on a.. dare i say it... agp plug, eww. and a C-Media AC'97 Audio Device driver vr 5.12.1.41 with Xear 3d 3d audio engine anyways with that out of the way, and the knowledge that this is my brothers computer, not mine of course, mine plays crysis on medium detail with no trouble! this Machine would die installing it. after being a bit long winded my problem it if i say in the settings it is a 4 speaker setup and plug the speakers into the blue line in plug they work! great for a little while, then he notices some games don't have sound, like far cry and gta, so is there a way to fix this problem or tell the computer to send all the audio out the line in jack thanks and sorry about being so long winded.