My 8500 has a dead PRAM battery so if I unplug it for any amount of time it will either not boot or not recognize the Radeon 7000 PCI card. But if I plug in a TV to the built in video out ports it boots as normal. Plus my machine has the G3 500MHz Sonnet card.

ADDING

Or if I do not have a tv on hand just keep restarting until it works, which can take a long time. Be glad you have a power button on your machine.