If you have this problem maybe other program is using the snd resource, so, you need know which is the program is using it. You can do it with lsof, and kill the process.
~# lsof | grep pcm ; lsof | grep dsp
xmms 17613 lexo mem CHR 116,8 12785 /dev/snd/pcmC0D0p
xmms 17613 lexo 10u CHR 116,8 12785 /dev/snd/pcmC0D0p
~# fuser -v /dev/snd/*
USER PID ACCESS COMMAND
/dev/snd/controlC0: lexo 5468 F…. mixer_applet2
lexo 18351 F…. xmms
/dev/snd/pcmC0D0p: lexo 18351 F…m xmms
/dev/snd/timer: lexo 18351 F…. xmms
* /etc/init.d/alsa-utils reset card
