You've killed the LCD panel.
Obviously you were always well behaved at school and never messed around with the screens on calculators.
From your description, the outer casing is intact, so it's probably just a case of getting the LCD panel replaced from parts (worst case, this will include associated circuitry if it's shorted or something, or not part of the same assembly, but unlikely in newer laptops).
Probably <US/GB/EUR> 80 to 100 plus labour.
Youtube vid of what needs to happen....