i've been troubling with this situation for 2 hours. i did some research and ppl keep telling me BIOS stuff. well i don't know how to configure bios. but i solved my problem
i have Asus P7P55D-E Pro with Via HD audio deck sound driver.
today suddenly my sound gone off.
and i can tell you honestly if you use windows 7 it's problem solver on management desk is doing a goddamn job on its own.
do these steps and you will get your audio back.
Go to My computer, right click and Manage. > device manager >
under the audio , video and game stuff find Via H.D. Audio > right click and remove it.
then right click on audio, video and game > search for hardware changes. ( u can do it from the top, just below the HELP tab) it will find that u have no audio driver, and it will install it by itself.
go to management desk > problem solver > audio.. follow the steps and say 'yes' to him when it asks to correct some wrong things about your audio.
i got my audio back this way, safe and sound.