Mac laptop screen gone black - solution
I called the Apple helpline about this and they took me through the solution:
1. Turn off and unplug your laptop.
2. Remove the battery.
3. Press down and hold the power button for 20 seconds.
4. Insert the battery and power lead.
5. Hit the power button and then immediately hold down P, R, Alt and the Apple key simultaneously until you hear the second start up beep.
Your laptop should then boot normally!