Go on the dell site and download newest drivers that they have. by the way i don't think it was necessary that you updated your bios just for that...anyways try finding new drivers or call Dell Support
I have a Dell D820. It has the Sigmatel 92xx audio. It was working in Vista Business and then I upgraded to Ultimate and it stopped working. I downloaded the latest BIOS and audio drive from Dell but nothing.
I uninstall the audio device from Dev Manager, did a hardware scan, vista installed it but still not working. Funny thing though is that it beeps. I mean, error popups or anything that needs attention it beeps. If you play song or watch movie, no sound

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