|Are you saying there is nothing on both built-in display and external screens?|
Does the laptop spin up/boot up when powered up i.e there are noises of the fans and the hard drive (even indicator lights too) showing "normal" signs of life?
Since both internal and external displays seem to be defunct.... (presuming you have tried the function key combination to route an display to external monitor correctly - and no joy there..) it may be that the motherboard has also been damaged; or possibly just the graphics adapter?
Dealing with the laptop display itself to start with:
Are you sure you've connected the ribbon cable (which feed to built-in display from the motherboard/graphics o/p) correctly/securely at both ends?
Have you located and checked the graphics adapter to see if it's still in place (if it's one that is plugged into the motherboard, rather than integral/soldered to it.