LCD becomes black at OS boot

OK - Try this, after booting using the keyboard brightness buttons lower the brightness to the lowest setting. Then slowly raise it does it light up? Also if you use a flashlight though Apple logo can you see your desktop image?

No, both operations don't show anything.

By the way, here are the graphics properties (with the external monitor L72D connected):

GeForce 8600M GT:

Chipset Model: GeForce 8600M GT

Type: Display

Bus: PCIe

PCIe Lane Width: x8

VRAM (Total): 128 MB

Vendor: NVIDIA (0x10de)

Device ID: 0x0407

Revision ID: 0x00a1

ROM Revision: 3175

Displays:

Display Connector:

Status: No Display Connected

L72D DVI:

Resolution: 1280 x 1024

Depth: 32-Bit Color

Core Image: Hardware Accelerated

Main Display: Yes

Mirror: Off

Online: Yes

Quartz Extreme: Supported

Rotation: Supported

Thanks

If you don't see a ghost image of your desktop with the flashlight your LVDS cable or the display is bad. As you replaced the display (hopefully with the correct one) then the cable is likely bad.

That was also my reasoning: I checked the LVDS cable wire-by-wire, and its seemed OK. What puzzled me in the graphics properties is: "Display Connector: Status: No Display Connected", as if the LCD doesn't enumerate.

It is a correct one, it behaves exactly as the original.

Did you put the LVDS cable in upside down? If you did, you might have blown the fuse links (near the connector) marked with a letter 'P.