Please make sure that the device is not set to disabled. Is there any exclamation point error or unknown device message (just like the image below) in the Device Manager? Was it working properly prior to the upgrade? You can also try a Windows System Restore to an earlier date when the sound worked.
I just want to know if the issue started after the upgrade to Windows 8. Was it working properly prior to the upgrade? There is also a possibility of corrupt registry entry for the audio device. You may try to check if Windows audio service is started and running. Please make sure that you follow the Windows 8 Clean Install Instructions for VAIO PCs. It is also possible, however unlikely, that the audio card has already failed even after trying a full format recovery.