Try this... Turn off the laptop, connect an external monitor, turn on the external monitor and then turn on the laptop. Can you see fine on the external monitor? If yes, then either the ribbon cable that connects your display, or the display itself, are going to need replacing. You will have to open up the device to see if the ribbon cable is the problem. If that isn't it, then the display will need fixing/replacing.
If, however, the external monitor also gives you problems, then your graphics card is probably the culprit.