That was my strange sound error. I found the problem. It seems to be a known bug,
that when you reboot and you have from origine auto-mute enabled in alsamixer,
shit happens (some-times).
If your sound is muted after boot, you can bring it back and control the reason by
entering in ssh :
what should bring back immediately your sound. To cure the problem completely,
and with the left/right arrows search for auto-mute. After, with up/down arrows
put it on disabled. I think it should be disabled already at the installation of the package.