On my MacBook air I am stuck on the boot-up screen (apple logo and white screen) I accidentally changed the permissions on Macintosh HD from "Everyone: Read and Write" to "Everyone: No Access" how stupid, I know. Anyway, I then turned the computer off (Even more stupid!) then when I attempted to reboot, I got stuck here, tried all the basics like SMC reset, PRAM reset. When I try to safe boot, the little bar at the bottom disappears and then the spinning gear also disappears. What can I do?