Hi I have a concern on my iMac.The 10.11 Beta is already installed and when I start I get an Icon with "?" inside. The startuo disk is not found.I try to start in recovery mode with cmd+R and the I get an icon with a locker inside and it ask me for a password.I would like to be able to reinstall compltely my mac but I cannot chose an otehr Drive to boot like USB for exemple.Please some body can help ?Thank in advanceePierre