Try re-installing the sound driver.
If still no sound, re-install the chipset driver, then install the sound driver after that.
You can get the drivers from the ASUS website, but not until Monday 18 August because their driver download service is currently unavailable due to essential maintenance. Here is the link when available on Monday:
http://www.asus.com/Motherboards/P5VD1X/HelpDesk/