Other Fn keys all seem to be working.

I'm on a Shuttle home-built desktop.

I installed 13.04 fresh, rather than upgrade; in 12.04, sound keys worked fine.

The sound icon in the top bar isn't the same either. It has the little speaker symbol that I'm used to, but to the right of that is just "---", where there used to be the little right-parentheses–type sound-waves symbol.

When I click on the speaker symbol, the drop-down menu appears, but the volume bar doesn't respond to my mouse clicks; it's stuck at about halfway. "Mute" is grayed out, incidentally.

When, from that drop-down menu, I go to Sound Settings, I can change the volume there.

It looks like others have had this problem and similar ones with 13.04. I haven't been able to make use of the answers I've seen.

Can anyone help?

Thanks.
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Update: The problem has gone. I don't know why. All that happened was that I shut down the computer and restarted.