did you remove battery? press cuda switch and try again? Just like the beige G3 they don't like change. Also how about the jumper block on the motherboard? Its set to the stock CPU speed, it must be bumped up and bus matched correctly with hard drive jumpers to work (like the beige G3's) If not it wont boot.

I think they changed that in the G4's with Zif but I forget exactly when It changed.

Hopefully I gave you some decent info that helps you in the correct direction.

BTW my first New bought by me Mac was a B&W G3 350 overclocked to 400 to void the warranty .