Always boot in -v mode when testing to see whats going on.
Try looking for any error messages or just the point where it stops.
If in -v mode it stops after changing graphics modes (when the console text disappears) the problem could be the graphics card. Only idea is try safe mode without nvinject or more recent release (10.5.6?).
You can use a modded AppleSMBIO is there nothing else available.