I had a similar problem in Fedora 3 after running the updates from yum. I updated the kernel and several programs no longer ran, including sound. Try reinstalling these files as root
from Disk 1 of the install CD:
run lsmod to make sure the soundcard drivers are loaded.
reboot to the original kernel
as root, run the following command: /usr/sbin/alsactl power [card#] [state] where card# is the soundcard number and state is on/off
in my machine I used /usr/sbin/alsactl power 0 on
my sound returned immediately after running this command
If still no sound, uninstall and re-install the sound apps, i.w mixer, CD and audio player.