i have a similar problem sometimes. i have an onboard sound card but i have that disabled in bios and i have a sounblaster audigy fx for my sound. sometimes when i update the graphics drivers, the soundcard doesnt produce any sounds at all. the drivers are there, from the look of it it should work but it doesnt.
what i do is this:
turn off computer and plug off the sounblaster audigy card.
start the computer and go right into BIOS, enable onboard sound card and let windows boot up.
turn off computer, plug back my soundblaster card.
start the computer and go back into BIOS and disable the onboard card, then let windows boot up. and i have sound.
