I had exactly the same problem you mention in this post. Perfect sound in all other audio applications (Clementine, VLC, even Internet videos) but no login sound or bell. It happened every time I'd install a new kernel.
What I did to solve it was:
1- Check that phonon-gstreamer is installed and working.
2- Run alsaconf and, even if it says it can't detect your soundcard, try setting it up with any of the legacy drivers it recommends.
Worked perfectly on my laptop. Hope it helps!