Graphics: Asus EN8400GS (Basically NVIDIA GeForce 8400GS)
My first core had a nVidia 8400 and although I didn't suffer from the black screen, the machine would freeze all the time.
I've since replaced the core with a completely new core and my second attempt went perfect, this time with a nVidia 7200 or 7300.
Since you're connected through the VGA out that eliminates us thinking it has switched to another output after booting.
I know it's a PITA to have to keep trying various parts, but I would try an older nVidia video card.