sound not working

Hi, I have a Compaq Presario 700 (I am assuming a 700US
as it does not specify), running the factory sound and
speakers. One day my sound stopped working. Completely. I
have installed new drivers, uninstalled new drivers, even
had a computer technician look at it, and they cannot
determine the cause of my problem. Windows XP's status on
my drivers and devices says that there should be no
problem with the sound, and yet no sound emanates from
the speakers nor from the headphone jacks. When I start
the computer up, the speakers make noise as power is
being supplied to them (that on/off blip noise that
indicates the speakers are on and working), and there is
no problem indicated by Windows. I HAVE CHECKED THE
VOLUME CONTROLS (there are two or three of them and I
have looked at all of them multiple times, there should
be no problem with the volume, my sound just refuses to
play). Also, my Windows system restore, though turned on,
is not working either - as I tried that in an attempt to
fix the sound. Norton Anti-Virus with up to day virus
definitions cannont find any viruses either. I am not
concerned about the system restore not working, just the
sound. This is a very strange occurance, and I want to
know if anyone can offer any insight short of telling me
to throw my computer out the window and buy a new one
(which I wish I could afford).
Jared