if you experience a sudden unexplainable loss of audio in fedora check GAIM,
it's taken me quite a while to figure out, but GAIM seems to be grabbing the audio /dev/dsp and keeping it to itself so you can't play mp3's in xmms or listen/watch a music video,
to fix, i checked my GAIM preferences and change the audio output from ESD to a simple console beep,
since i've done this, my audio has never disappeared yet (fingers crossed) and prior to doing this it would go awol on a very frequent and rather annoying frequency