Your mixer defaults muted, IIRC. So you have to set it to unmuted, and at a certain volume; then you also must place "alsactl restore" in /etc/rc.d/rc.local so that on each subsequent reboot your volume is restored. Here's a thread where Excalibur (The resident Slackware Guru) helped me out:
http://www.linuxquestions.org/questi...threadid=30609
regarding a similar issue. It might apply to your situation and help fix the problem
Cool