Diego, if the external monitor worked, it is time to open up your laptop. Check the cables going from the motherboard to the LCD, check the inverter for obvious damage. It is possible that the backlight got damaged, check with a flashlight angled against the screen and see if you make out any shadows etc. If your cables are properly seated, and your inverter is okay, I would consider changing the LCD. Follow these guides to work on your laptop.
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