I have a habit of disabling my mic and camera drivers when I am not using them, so I was surprised when after the latest windows update, which re-enabled cortana, I accidentally clicked on it, and it started responding to me!
Preplexed, I check the status of my driver in the device manager. Nope, it was still disabled.
Searching around, I found that the issue was my "Realtek(R) Audio driver", under the section "Sound, video and game controllers". Which is very misleading. Both the drivers show Realtek, but I did not have time to search what difference they have. Anyway, I tried disabling the new driver.
However, now the mic was disabled, and "Hey Cortana" did not work anymore, but the audio was gone too! What kind of design is this??
I think I will start looking into it tomorrow, but very confusing all the same.