This is the email that I received from the seller..
Due to recent windows update once sound is muted by Fn+F4 key combination it stays muted. We've noticed this last week and already updated our master image.
To resolve this you need to do the following:
and download "Hotkey Appendix Utility"
Run it and it will extract to c:\util2\ , go to the folder and run setup/install file.
After reboot press Fn+F4(mute/unmute) key and sound will be back.
However you will notice that now screen brightness cannot be adjusted. Video driver update is required to resolve.
Go to: http://pc-dl.panasonic.co.jp/dl/docs/017093?dc
and download "Video Driver"
Run it and it will extract to c:\util2\drivers\video
Go to that folder and run setup. After this reboot and both sound and screen brightness adjustment should work(fn+f1/f2 keys).
Please let me know if these steps solve the problem.