My iMac has a broken screen which doesn't allow me to view anything. So I got a monitor and connected it to the Mac and it works great. My problem is when I boot up my iMac it won't display the grey screen with the apple logo loading into the OS. It simply stays black until it's at the login sequence of the boot. How can I make my iMac be able to display the whole booting process? I tried using the Mirror Displays and that did not work for me. I also read if I don't select the mirror option it should work, but that did not work for me either. I want to able to factory reset my iMac but I can't do it because I can't see the booting part of my computer which is where I get to partition the drive and wipe it clean. Any thoughts or suggestions on how I can fix this?