MacBook Pro 3.1 internal (replacement) LCD not detected by graphics card; external monitor OK My MacBook Pro (2.4 Ghz, Santa Rosa with infamous nVidia card) acts strange. I replaced a cracked screen with a new and since then I have been loosing my mind over this problem:It shows the normal gray screen with Apple logo and animation flawlessly during start up but the internal display goes black without any rendering at all when all is loaded. (shining a light on display show nothing) If an external monitor is connected through the DVI port it will remain black during start up and then show the desktop as the internal display goes black. This happens both while booting to Mountain Lion and Windows XP. I have checked "About my Mac" and only the external display is listed. The same is the case if I use the nVidia Control panel in Windows XP. The mirroring works in Windows XP although with distortion.

My questions: Is this a hardware problem or is it related to software maybe even firmware? What controls the display during start up, graphics card or something else?
This sounds like a hardware issue, but there might be a few things you can try.

I would boot the mac with the cmd+v keys to show a verbose output. If this doesn't work, you could try resetting the NVRAM/PRAM (docs can be easily found on the apple site)

If you don't see the Internal Display in the about my mac app, the Display Data cable might be improperly seated. There is a fairly good tutorial on iFixit.com http://www.ifixit.com/Guide/Installing-MacBook-Pro-15-Inch-Core-2-Duo-Models-A1226-and-A1260-Display-Data-Cable/1312/1