Have you tried playing audio without the headphone? sounds working?
I have seen many other people complaining that after a reboot suddenly audio function stops functioning.
It may occur in G400 and G500
It may occur in windows 8 or windows 8.1
Well I am sending you a couple of remedies, hope they work, Try it
First things first
Update the audio driver, which you already did, so the next step is Uninstall KB2962407 update
Navigate to [ control panel ], then select [ windows update ], then select [ view update history ] then select [ install updates ]
but if KB2962407 is installed, right click the update to uninstall
According to the different operating system, finding the right menu might be difficult to find, so try your level best.