My MacBook Pro (2.4 Ghz, Santa Rosa with infamous nVidia card) acts strange. 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.
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?