No audio, Sound mixer missing....

Hello,
I recently lost sound on our Dell Vostro 1500 with xp. I done a system restore, reinstalled audio devices and tried just about everything else and still no sound. It happened after we ran a scan of the computer. The sound controlls are missing off the tool bar, when I go to the volume control in start menu it says I don't have an active mixer and to install one which didn't work either and when I go to control panel and sound and audio device everything is grayed out, with no default device set and I was unable to set one. I have Sigma Tel High Definition Audio Codec and it's enabled to run. Please any help you have would be very much apprecaited