So I created a bootable USB of mountain lion so I could do a clean install. I did the same thing for lion and had no problems. When I boot while holding down the option key, I get a grey lock screen that just has a space for a password. My admin password isn't working. I've tried others but no go. I thought there might be something wrong with the USB so I tried booting in recovery mode with command+R. Same thing. Does anyone know what this is? Sorry if its a stupid question.