If what they suggested does not work try checking to see if you have an update to one of you sound drivers. You may have already tried this.

control panel>
system>
hardware>
device mgr
look at the audio
Go into properties for it and update the driver.

Also check out this link for a trick that may help you..

http://www.mydigitallife.info/2007/08/15/adobe-flash-no-sound-wavemapper...