The first thing that comes into mind is the screen's backlight has failed which means the screen needs to be replace since the backlight is integrated into the screen.
The other thing could be the screen's video connector has somehow come loose and needs to be inserted back. This is unlikely since the connector is usually pretty secure. The only way to check and fix the issue is to take apart the laptop. Specifically, the bezel around the screen needs to be removed. There are special tools to do this that are typically made of plastic; I do not know what they are called. But there are Youtube videos showing people how to remove the bezel using a credit card.
You can do a search on Youtube to see if anyone created a tutorial to replace the LCD screen that is specific to your laptop model. But the steps are generally the same for most laptops.
When in doubt, let a professional handle it because if you are unsure and uncomfortable taking apart electronics, then you could actually cause damage to the laptop.