As it's OK with an external monitor, the problem is most likely the backlight. If you can see a dim screen display when shining a light on the screen, the backlight power supply (inverter) needs to be replaced.
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Thanks for the response.
Unfortunately, do not see a dim display, even if a flashlight is directed to the screen.
If I make the room completely dark, the backlight itself is visible, even though nothing appears on the screen. This is similar to if the computer is on standby.