which toshiba? certain toshiba laptop has this switch inside the screen that automatically turns it off and will not turn on until a restart or something similar.
can you turn it back on when you type or move the mouse cursor? or does it not turn on completely?
if it turns on if you move the mouse,
right click on the desktop>properties>screen saver
see if it is turned on, if so, turn it off, then on the screen saver dialog, click on "power"
then on the bottom, you should see where it says "turn off monitor" and it will given a certain amount of time, same for hdd, and standby, you can turn off monitor and standby if you would like it to not black out.