HELP! 1.25 DP G4 WILL NOT BOOT, FANS AT FULL SPEED!

[frixr4kids]

I am piecing together a Mirrored Drive Door G4 Dual Processor 1.25Ghz, but I'm running into some problems. I have sucessfully booted the computer once. It turned on and booted to the screen with a question mark (i.e. looking for an OS to boot). I turned it off and the next time I turned it on everything seemed normal, but I got no video and any drive plugged into the logic board wouldn't power up. Finally, 15 seconds after I turned on the computer all the system fans began to spin at FULL SPEED! Resetting the PMU, switching the system battery, unplugging the drives, switching video cards, RAM, etc. nothing changes. The computer continues this until I cut the power to the computer. Does anyone have any ideas, suggestions? Thanks!