Try turning off the laptop, connecting an external monitor, turn on the external monitor and then turn on the laptop. Can you see your desktop on the external monitor?
If no, then you are probably going to need to replace the graphics card.
If yes, you can see on the external monitor, then you need to check the attached display. First by checking the ribbon cable that connects the display. Is it bent, pinched, loose, damaged, torn, etc.? If no, then the display itself may need replacing.
NOTE: Do not open up and mess with the device if it is still under warranty. In this case you would be best to contact the manufacturer to repair or replace it.