Well, if you can't do it through software (Energy Saver control panel), I think the Quadra 700 had a circular power button with a slot in it. If you push the power switch in, and use a screwdriver/coin to rotate the power switch, it should stay "stuck" in the down position, and will thus restart the system in the event of a power failure. Like I said, I'm not totally sure if the Q700 has that style of power switch, but it's worth a try.
Cheers,
infiniti