Out of nowhere yesterday too I lost my onboard Soundcard Creative Core3D. I did not change anything in BIOS, For 10 weeks the motherboard had a normal working onboard sound. The only solution to get my onboard sound back was pressing the CMOS-Reset button. And I got my sound again
What was the problem? I never lost the onboard sound on any other motherboards and I never had to reset BIOS, never ever, till yesterday.