How to activate external display when Macbook display is dead I have a Macbook which I bought in the fall of 2009.  I recently upgraded it to OS X Mavericks via the free download.  The display has been flaky for a few months; the mouse worked and you could click buttons and close windows and so forth, but the image would sometimes flicker or slide back and forth.  So this made me think that the problem is with the display and not the CPU or anything like that.  Well now the display is totally dead, it gives me nothing but vertical gray bars.  

I have an external display connected via HDMI adapter, but the computer is not sending a signal to it.  Is there someway I can force the computer to send the display image to the external monitor, like say by holding down a particular key while booting?

Thank you to anyone who can advise me.  I can't afford to buy another computer right now.
Pressing Command + F1 should enable mirroring of the internal display to the external monitor.

Once that is enabled you can go to System Preferences to tinker with more advanced stuff like resolution and refresh rate.