Why my screen is not working

Hi @umarkhan15083

With the laptop turned on, but no display shown on the screen, try shining a flashlight at an angle close to the screen and check if you can see any images at all on the screen.

They will be very faint if they are there so trying this in a darkened room may help to see them.

If you can't see any images at all on the screen, and since there's a display showing when the laptop is connected to an external monitor, then the problem is either a faulty LCD panel in the laptop or a faulty LVDS cable between the LCD screen and the motherboard.

Here's the hardware maintenance manual for the laptop. Go to p.62 (66 of 73 pdf) to view the procedure to remove the LCD panel. This will also allow you to check if the LVDS cable is OK or not.

If you can see images on the screen, then there's a backlight problem. This could be due to a faulty LCD panel, a faulty/loose LVDS cable or a problem with the backlight power supply on the motherboard. Further testing, possibly using the motherboard schematics, would be required to determine where the problem is.