Hi all, i read all your posts looking for an answer to the same problem, luckily i have found the answer elsewhere and it solves the v annoying issue within minutes, which is highly frustrating as like all of you i have spent hours trying to solve!

Simply! Go into device manager and select sound, then right click and select properties.
Then select the driver tab from the top and click on unistall (advanced) and follow through the instuctions.
Reboot your system and allow windows to find new hardware and install the driver. (make sure your connected to the net for windows to download driver)

Problem solved! Hope this helps

Matt,