Startup disks are disabled after upgrading to OS X El Capitan Recently I upgraded my Mac mini to OS X El Capitan. After the upgrade completed, I can't select a startup disk in System Preferences -> Startup Disk. 



BOOTCAMP/Windows is disabled here. Searching for a solution I came across the following: press and hold the Option key while booting to get all available systems, but that trick didn't work for me. Any solution will be highly appreciable.
Click the lock to make changes