try these:
start > Run > at the search box type services.msc.
at the services window,scroll down to Windows Audio.
click once & at the upper left portion,you will see:
Stop the service
Restart the service
click Restart the service,when done close the services window
& try the sound.
if still no sound,double click the "Windows Audio" (Services) click
the Stop button,at the startup type box,select "Automatic"
then click start button.click OK,close the services window
& try the sound.