Reset Audio Configuration (User)
Sometimes the user config breaks down and HDMI does not get sound anymore.
Restart User Audio Daemon
To reread the config files ~/.config/pulse/daemon.conf and /etc/pulse/daemon.conf, do this:
Missing Audio Devices
When missing audio playback or capture devices this might do the trick.
To reset the audio user config do this:
Conflicting Modules
Module module-switch-on-connect.so can cause the pulse daemon not to start.
Remove module-switch-on-connect.so from file /etc/pulse/default.pa.