I converted to Windows 8 and now I do not seem to have the “Stereo Mix” setting on the Recording tab on the Sound page. I have right-clicked on white space and checked the Show Disabled Devices and Show Disconnected Devices. No Stereo Mix; just a couple microphones, my webcam and Digital Audio (S/PDIF) choices.
How did you convert - install Windows 8 to replace the previous Windows version, install Windows 8 in another partition, or buy a new computer with Windows 8 installed?
If you installed Windows 8 on the same machine then you probably need to see if you can get updated sound device drivers meant for Windows 8, made by the computer or motherboard manufacturer. See http://wiki.audacityteam.org/wiki/Updating_Sound_Device_Drivers .
If you cannot get Windows 8 drivers, Windows 7 drivers may work, including any that came on a drivers CD with the original computer. Windows 8 audio is near-identical to Windows 7, but it’s possible the Windows 7 drivers may not have been recognised by Windows 8, perhaps because of some digital signing issue.
When I installed Windows 8 on my Windows 7 (HP) laptop, I found the built in audio device had gone back to drivers made by Microsoft, with the only input being the built-in mic. My solution was to run the Windows 7 audio drivers installer from the Windows 7 partition, which installed the HP-supplied audio drivers on Windows 8. The audio device now functions exactly as it did on Windows 7.