I had ALSA working fine, outputting through the SPDIF port of my motherboard to my surround stereo. I literally didn't touch the computer, and it stopped working. All applications, eg mplayer, amarok, seem to think they're working fine, but there is no sound coming out of the stereo, or even the analog ports on the motherboard.

Alsamixer is working fine, and I've set the IEC958 volume to zero as is required for some reason. All of the modules are loaded. I've reinstalled the kernel, run alsaconf, installed the Realtek drivers, but nothing seems to work. I've checked from Windows XP that there is no problem with my hardware.

I don't know what to do short of wiping the partition clean and doing a fresh install, but I really don't want to do that. How should I go about figuring this out?

Here's a couple details:
Asus A8N-E nForce4 motherboard, with Realtek ALC850 chip
Kubuntu 5.10
Kernel 2.6.12-10-amd64-generic