That sounds very odd, and having a blank disc in a drive will not prevent startup. Did you try unplugging the machine (including all firewire devices), waiting a few seconds and plugging it back in? I have a G4 Mac that did something similar. After years and years of service, it refuses to even turn on. Well, it will power up if I let it sit idle for about a day, but if you power it off again for any reason, it needs to wait a day before it will turn back on again.

I've never even heard of auto shutdown, but I know if there were indeed such a feature available, I'd never, ever enable it. I've never used any of Apple's tech tools (other than Disk Utility which is included in the OS), just Alsoft's Disk Warrior which seems to solve minor problems from time to time.