I can't remember exactly when this quit working, or if it coincides with anything I did to my system. I'm running OS 10.4.11 on a G5 Quad and have a really weird issue:
My keyboard controls for changing the audio volume work just fine. The on-screen volume indicator (speaker and little bar of blocks) appears as well. But the blocks never change color to indicate the volume level!
I can't figure it out, despite lots of googling and other searching. Now I notice a few of my screen savers quit working as well. Argh.