Question: Can't open system preference panes after upgrading to El Capitan
I ran the upgrade on my mid-2008 MacBook Pro to take it from Yosemite to El Capitan. I've had two major issues. First, El Capitan forgot all my e-mail passwords which I have tried to manually re-enter into Mail. But the more troubling problem is with System Preferences. When I try to change the loudness of sound on my MacBook Pro, it shows that the sound is muted and the screen flashes. I went to the Accessibility pane to try and turn off the flash and see if that would fix the sound, but the pane will not open. I click on it and after a period of several minutes, the OS responds that it cannot open the preference pane. I then tried to open the Sounds preference pane and the same thing happens...after several minutes, the OS says it cannot open the preference pane. I've tried re-starting the MacBook Pro to no avail. I see that system preferences cannot be repaired. I have no idea on how to fix the preference panes to open properly. I tried re-booting to the recovery partition and running Disk First AId. It found no problems, but it didn't fix anything either.
Any ideas on what I can try to get the functionality back on my machine?
MacBook Pro, OS X El Capitan (10.11), 4 Gb of RAM