The way laptops monitors work is to produce an image that is in reverse... dark is light. Light is dark... colors are opposites of what needs to be displayed.
This situation is handled by a device called an inverter, which is about the size and weight of a felt tip pen with a socket or plug on one end.
When the image is sent to the screen, it is not viewable because the colors, light, and dark are reversed.
This inverter converts the screen from negative images to positive images.
When screens are sold, they usually do not have the inverter, or they have an inverter that is worn out, or is not the correct one for the combination of the screen and the computer drivers.
The are expensive from the computer dealer, about $50 to $60, but are very inexpensive on eBay, discount shops, and parts suppliers...
But the inverter MUST be the correct one to work with the screen, motherboard, and driver output. You can usually buy them for $8 to $15, but you must have the correct one... It is about the same size as a felt tip pen, but is actually flat or rectangular and wrapped in several layers of plastic material... and has a plug on one end that has to match the socket on the screen or vice versa.
It may be that the screen is not the same as the original screen, or that you have no inverter module yet, or the one you have is burned out.
First, get the brand and model of screen from the info on the label on the back of the screen, then see what is required as inverters go. If it came from the same model of computer as what your replaced, it is easy. If the monitor screen came from a different computer, manufacturer, or graphics specifications, it can be difficult.
It might be worth while to have an accomplished computer tech look at it, or test a few inverter cards..