My screen was cracked, and I replaced it. Now, the screen stays lit for about 30 seconds on start up then the backlight shuts off. I can see the screen output with a flashlight, so it is still working wtihout the backlight. Also, once it shuts off, If I close the screen and open it again it will illuminate for about 5 seconds then shut off. It does this everytime I open and close the laptop. The cracked screen always stayed illuminated, so I am wondering if this replacement is defective. The only thing different with this screen that I can tell is that the cable going into the inverter uses an extension to make it reach. My original screen did not have an extension to the inverter. I wonder if this is causing it? It is long, so I had to stuff it in the cracks to get the bezel on. Not sure if this would cause this symptom.
If the screen will light up, even temporarily, and no other changes were made other than swapping out the screen, I'd suspect a bum inverter. Get in contact with whoever sold you that screen and get a new one.