I've seen a couple occasions whene sound modules loading out of order prevents it from working.
For instance, you have a sound card and a modem with audio support in your PC. If the sound card modules load first, you are OK, but if the modules for the audio portion of the modem load first you get no sound from your soudncard. This will be random depending on which device gets recognized first at boot.
check out this page, relating to multiple audio devices and alsa, and how to work around rthe issue.
Let us know if this helps.