first go into device manager , uninstall all ac97 drivers for the sound, reboot. Then reinstall. Also, make sure you have all windows updates. You may also have to enable it in CMOS. It may in fact be your onboard is bad and you may need to buy a sound card instead but I don't know what board you have, so I can't say for sure. Give some more details of you pc, thanks.
I reinstalled XP on an old hard disk and now my sound is shot
I installed the AC 97 driver, the one that is supposed to go with my board, and it says device cannot start.