Hopefully downloading the newest drivers from http://support.asus.com/download/download.aspx
will do the trick. If not, having a quick read through http://windows.microsoft.com/en-US/windows7/Tips-for-fixing-common-sound-problems
will give you some more options for fixing sound problems in Windows 7. Since you have already run the troubleshooter, move right down to "I've run the Playing Audio troubleshooters and I still cannot hear sound from my computer" section.
Hope this helps!
Microsoft Windows Outreach