The system preference panes will not load When I open System Preferences and click on an item it says 'Loading Users &amp; Groups' at the top of the window, but will not load the pane.

I've tried deleting the property list file: 

 /library/preferences/com.apple.systempreference.plist 


I also tried clearing the PRAM and booting in Safe Mode.
Sometimes it's just enough to quit the System Preferences app. Check if the process was ended well, i.e. use Activity Monitor (also to quit &quot;System Preferences&quot; app). In my recent case it was not necessary to force quit, just select the process and quit was enough.
Alternatively Force Quit if System Preferences is open and in the Doc, just do a secondary click on the System Preferences icon, hit [alt] key &quot;Quit&quot; will change got &quot;Force Quit&quot; and click that.
After restarting the app the preference pane (in my case time machine pane) could be loaded as expected.
Lately it happened, that the described method didn't work, after force quit I still couldn't open the preference pane. I found that waiting a little (few minutes) before reopening helped, because when I was not able to reopen the pane I searched for a different solution, coming back to System Preferences – without doing anything else – was able to open the desired pane.