Niner since 2012
uhum hum, It's f12 Golnaz :).
Wow, the lady is truly enlightened.
@"How to turn off HDMI default audio device." question:
Try disabling your HDMI audio playback devices.
I don't think it'll re-enable itself.
I used to connect my laptop to my TV with HDMI and used optical for sound .If I remember correctly disabling HDMI sound got rid of that problem.