One troubleshooting step is testing the video output on an external monitor (or TV). You can connect your laptop to an external monitor using VGA cable, DVI cable, HDMI cable or S-Video cable, it depends on a type of connector you have. Most models have a VGA connector, so it would be the most common way to connect. Some laptops detect external monitor automatically and start showing images on both screens right from startup.
Other models can detect the monitor but display image only on one screen (internal or external). In this case you’ll have to switch video between internal and external using the Fn key and one of the F* keys in the top row of the keyboard.
The screen receives data signal from the motherboard via LCD cable. If the LCD cable is not making good connection with the motherboard, it might cause image or colour distortion on the screen. Try reseating the LCD cable connector and see if it fixes the problem. Make sure the LCD cable connector is plugged in correctly. In most laptops the LCD cable connector located under the keyboard bezel ( keyboard cover). If it’s not there, most likely you’ll find it somewhere under the keyboard. The LCD cable runs inside the display panel, under the screen. For this test it’s necessary to disassemble the display, so you can access the cable. A pinched or damaged wire inside the cable also can cause colour distortion.
Try applying some reasonable pressure to the top part of the display assembly. Squeeze it with your fingers. If the screen starts showing different colours, lines, or clears to normal when you squeeze the top part of the display panel, most likely this is screen failure. In this case you’ll have to replace the screen.