Hi folks, my Mac Pro doesnt boot anymore. When I switch it on I can hear the HDD spinning up but that is it. The screens remains black. I connected the screen to an existing Powerbook to make sure that one is working. All the other parts seem to work normally. Like the fan blows etc. But the system does not boot. I cannot even open the optical drive. I think the keyboard does not even get power. What can I do. Or even better, what is the problem here?