Thank you bnice.
I did what you post me, but the problem still exists.
Running alsamixer after startx does not restore nothing.
There exists two alsa configurations: one as user with Master muted and PCM 100%, and the root one with PCM muted and Master ok.
I don't know how to fix it.
It seems it load alsa config from.... i don't know
It discard /etc/rc.d/rc.local.