I have a 2012 MacBook Pro with retina on the sierra os. Last night I went to turn it on and I thought it was starting fine- I saw the apple logo, then it went to my login screen, I typed the password and then all of the sudden it went back to the apple screen like before and made me type the password again except this time it froze on the login screen. I rebooted it and it did the same thing. I tried booting it in safe mode. I did the disk utilities and had it check out everything and it acted like everything was ok. I tried to restart it again and kept booting up in safe mode. It won't go back to normal startup. My question is does anyone know why my computer wouldn't let me login correctly in the first place? Why did it go back to the apple logo and then freeze? And why will it not let me get out of safe mode now?