My Mac Pro Laptop's monitor does not light up, stays black. OS X, 2.2 GHz CORE 2 DUO/ 2 GB/128MB vram. I can hear it turn on and when I click the volume buttons I can hear the chime indicating that it's working but the monitor remains blank. I've tried connecting an external monitor with no luck, but I think that might be because to use an external monitor it has to be set up from my laptop which I can't see to do that. What can I do to determine what might need to be replaced?