Thanks for reading!
I changed my OS X’s language to Japanese. Now some of the System Preferences can’t be reached anymore, for example the Sound section with the speaker symbol. I can click on it and it shows the Japanese name but nothing happens. Strangely all the third party entries still work as well as Quick Time and the Screen Options.
When I change them back, everything works.
Mac OS X 10.5.8
Mac Pro 2009