I turned off the defaullt monitor now I cannot get the screen to come back on

[rtsaturnsl1]

I turned off the default monitor option on my computer now I cannot get the screen to come back on after boot up

 

[the great randini]

reboot press f8 repeatedly> select enable low resolution mode> adjust settings >reboot

 

[alvine]

plug in external monitor, right click on desktop and configure your displays