So why do you think replacing the screen will make a difference?
If you're sure you see an image using the flashlight then you know the screen and the LVDS cable its self is less likely to be the issue.
So what could be the issue then? You’ll need to inspect the logic board LVDS connector to see if the connections are good (often times corroded). Then, you’ll need to test the fuse link to see if its still good as well as the backlight logic.