I encountered few times of a problem when I closed the lid but could not get the screen turn on. When I was travelling on a train working with my laptop, I need to close the lid when someone to get off the train. Then I opened the lid but the screen was turn off, the powere was still on. No matter I pressed the space bar, enter key, power button...etc, the screen was still dard. Any idea how do I get the screen back in this situation?