Solve Macbook pro black screen while booting

My Mac is 13'
version 10.9.2
2.8 GHz core i7
8GB 1600 MHz DDR3

After hours of trials:

I did the below and it worked:

1-Press and hold the power button for 10 secs to make sure your mac is off.
2-Press the power button then hold command+P+R.(you should hear startup sound).
3-Hold the power button to switch your mac off.
4-Remove your laptop cover (the laptop cover if you bought any) and flip it upside down for a couple of seconds (20 secs).[and YES this is THE KEY in my case].
5-Hold power+control+option+shift release then press the power button.


Note: The Mac was not connected to the power source.


I hope this would work for you ;)