You may want to open it back up and make sure the ribbon cable that connects the display didn't get pinched, bent, dislodged, etc.
Should nothing be loose, etc., then try turning off the laptop, connect an external monitor, turn on the external monitor and then turn on the laptop. Can you see your screen on the external display?
If it does show, then your display may need replacing. If it doesn't show on the external monitor either, then the graphics card is your problem.