Screen shutting off and refusing to turn back on

[quinn]

I use Ubuntu on a laptop, and sometimes Ubuntu shuts off the screen, and 
I cannot get it to turn back on.

I know that it shuts the screen off if I shut the laptop far enough, so 
I now have to carry it around with the screen in the fully upright 
position if I want to move it.

Sometimes it also turns the screen off for no reason that I can 
determine.  It is not a result of leaving the laptop unused for too 
long, because sometimes I can leave it for a long time and it is fine, 
and sometimes I leave it for a much shorter time and I come back and the 
screen is off.

I have tried turning off the "save power by turning off the screen" 
option.  I have tried going to another virtual terminal (which fixed 
this problem for someone else), and I have no other virtual terminals, 
despite the fact that that is supposed to be the default, and there is 
no way to turn on virtual terminals.

The laptop is a Toshiba 5105 S702.

How can I make the screen stop turning off?