This appears to be similar to this bug. Plugging the second screen (HDMI) is not recognized at first; selecting System Tools->Settings might be a trigger.
Second screen gets some action (background, maybe a stray window) and the main screen goes dark and stays dark. After some investigation, logging in from another computer and the magic gdm3 restart will bring the main screen back from the dead. -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]
