See you try to use Windows project to's display/TV system. As such my ideas are:
2. Set the speakers to what you had before.
3. Reboot, try again.
Clicking on the the Sound button in my System Tray does not provide any more the slider for changing the sound volume.
(I tried a few different ways I could think of such a going to the Control Panel to rectify the matter, but did not succeed.)