I suspect the backlight fuse link is burnt. To verify put the new display back on your system and then shine a flashlight through the Apple logo (a poor mans backlight). You should be able to see a faint image of the desktop. The other way is to plug in an external monitor.
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=== Update (10/26/2015) ===
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Not good :-{ that implies the display is the wrong unit for your system. What is the part number you used?
I suspect the backlight fuse link is burnt. To verify put the new display back on your system and then shine a flashlight through the Apple logo (a poor mans backlight). You should be able to see a faint image of the desktop. The other way is to plug in an external monitor.