If waking it from hibernation by pressing the power button doesn't work, try a powerdrain (turn off the laptop, unplug everything, remove the battery, and hold down the power button for 30secs. Put everything back in and turn it back on.). If that doesn't work either, it might be a problem with the video cable being pinched by the hinge. Either take it apart and see what's wrong (if you know what you're doing) or bring it into a repair shop.