After upgrading my Linux, I've got sound lost. Everything looked ok -- all the modules are loaded, all the special devices are created, no complaints in logs, -- but no sound.
Everything looked like the sound was muted (switched off).
Finally, the solution in found: in "alsamixer", the base of the bars "Master" and "Front" (and probably of some others) should contains the letters "OO" instead of the letters "MM". From the man-page:
When a mixer control is turned off, M (mute) appears below the volume bar. When it's turned on, O in green appears instead. You can toggle the switch via m key.
The problem is easy when you know the solution.