hi residual-self,
You could try running system file checker to check for any corruptions before you try the change to the power settings. I did this a couple of days before changing my settings as described above and it found some errors, but the sound problem still existed, so I can't really say the system file errors where related to my problem.
Just in case you don't know what I'm talking about....I've never had an issue using it, but it might be a good idea to back up your computer first.
from Search type "cmd.exe" in apps
right click on the cmd.exe icon, click on "run as administrator" located at the bottom of the screen.
type "sfc /verifyonly" if you just want to see if there are any errors without making any changes (you can skip this step if you want)
type "sfc /scannow" command to repair the damaged files.
After that I would restart your PC and then try my change to the power settings again, and if that doesn't help go through the usb troubleshooting guide from step 1 again.
Also if the sound always stops while using the internet, it could possibly be a problem with the flash plugin with your browser...i found quite a few other forums where users where describing this problem while watching youtube clips. If this is the problem I think your sound would die only while or shortly after browsing the internet. I couldn't see it applying in my situation as my sound died at anytime.