I hooked up an external projector display to an iMac. Then I made a setting change that made the screen black. How do I get rid of the setting? Safe mode allows me to use the external display properly, but when I go back in as a user it goes back to the black screen. Is there a file I can toss? Also, I created a new user account and it goes black on that account as well so this is a system setting issue and not user specific.