I have a Macbook Air Mid 2013 running Yosemite. My main display is broken due to an accident, but I have been successfully using an external display (thunderbolt to HDMI or thunderbolt to VGA, both works, no problem). I wanted to make a Bootcamp installation and I have no problems with creating the USB and such. The problem is, I can never get the startup options screen (after pressing 'option' on chime) to be displayed on the external monitor. My external monitors only pick up the display once I get into the user selection for MacOSX. Using a few tricks, I have managed to get the monitor to display Recovery Mode(command + R), but never the Startup Disk selection menu. I sort of need Windows at the moment, and this is driving me nuts. So I need to know, how to force the Mac to show the boot up / startup screen / startup disk selection / apple logo / on an external monitor? Thank you.