Dual 2.5 G5. Been having a similar problem to this for about 6 months now. After I reboot it (or there is a power outage), when I turn it on, I get black screen, no chime and the 2 rear fans slowly spin up until they sound like they are running at 100% each. It's like a jet engine in here! Previous fix was to hard reboot (hold the power button for a few seconds to shut down and then hit power button to turn on) and then it would boot up normally. This morning I came in and both fans are running full bore. Nothing on the screen. I figured we had a power outage over the weekend and when It restarted itself this happened. However, from looking at the other computers, there doesn't appear to have been a power outage. Also, that machine normally shouldn't have started itself back up anyway so not sure whats up. I've hard rebooted it several times this morning and I get all the same stuff. I don't know where the discs are that came with the machine at the moment but any ideas? It's running 10.5.6 or something like that.