display will not turn on after being turned off once

[duderonomy]

Hello,

I am using xfce4 but unfortunately I cannot see my desktop
due to the LCD not illuminating (turning on).

This occurs after I turned off the laptop's display via the xfce4 control panel Display.

There are two usability issues here. It would be great to solve them.
Please grab one that you know about (lol!) and tell me where to look for solutions.

I have two displays on a Lenovo T420 laptop. One is external monitor.

1. When both monitors are "enabled" and on, there is a dark outline
in the desktop (like two desktop backgrounds on top of one another
with transparency such that together they appear darker).

To remove that "super-imposed" image of the laptop's background off the
external monitor, I disable the laptop's display. Poof! the rectangle that was
in the external monitor's desktop background goes away.

So that's the lame way I use the computer:
Connect external.
Bring up the control panel and disable the laptop's internal display.

2. The big usability issue occurs when want to use the laptop's screen
and disconnect the external. It does not enable or turn on when the
control panel is used to turn it on. I do not know how I can enable the
screen without effectively restarting the computer...
I do not remember if restarting X will make it turn on. (can't test that, at this moment)

I am hoping someone can tell me how to enable the display via command line.
I can ssh into the box. Otherwise, I am unable to control it.

Is there a command line utility to do that?
I'd like to return to my work/desktop and eventually do a proper shutdown.
Last time I shutdown hard, a some applications lost their preferences (such as pidgin).

Any ideas?

Thanks!