laptop screen went off

Try pressing Fn+F4 and wait a few seconds to see if the screen comes back on.
You should try this up to 3 or 4 times if it doesn't come back on. If that doesn't work, I don't know what it could be.
 
Try connecting it externally if you can via a VGA or DVI or HDMI cable to see if it will show up on another monitor. If it works then more than likely the screen needs to be replaced or the light bulb of the screen. If it does not come on, then there could be something wrong with your video driver or video card.