The laptop starts but the screen remains very dark. You can hear a normal startup sound even though the screen is almost black. If you look on the screen very closely under the bright light you can see outlines of normal desktop images.
1. Inverter board failure.
2. Screen backlight failure.
Possible troubleshooting steps and repair solution:
1. Most likely this problem is related to the inverter board failure. The inverter board works as a power supply for the backlight lamp inside the LCD screen. When the inverter fails, the laptop starts normally but without a backlight on the screen. As a result, the image on the screen is so dark that you can barely see the desktop image. You have a good chance to fix the problem by replacing the inverter board.
2. If a new inverter board didn’t fix it, most likely you have a faulty backlight lamp inside the screen. You can try replacing the backlight lamp but it’s not easy and should be done only by an experienced technician. Otherwise, replace the whole LCD screen.