Also, if that doesn't work...
I had my Accounts pane disappear and I had two Universal access panes. Knew not why. Tried to delete com.apple.systempreferences.plist and caches. Did not help. I also have third party panes installed like PowerMate, WindowshadeX and USB Overdrive. I took those out of my PrefPanes folder in System. Relaunched system, and all was ok once again. Then after quitting it again, I moved my prefpanes back to where they belong, and I had everything back.