G4 in a coma

[btfarmer at optonline.net]

After replacing my (crashed) second hard drive, my nice G4 dual 533 will not boot up. 

I turn it on, I get a startup tone, the fans go on, the light on the front goes on. Then: nothing. No hard drive activity, the screen stays totally black. It will not boot from any CD either.

The weird part: I took it to Tekserve in NY, a guy there started it at least twice... successfully! Told me it was probably just a power surge, nothing really wrong with it. Just needed a few hours unplugged. I took it home, and booted it myself. 

It started fine - once - then went black again when I restarted!!  It was like that Warners cartoon with the singing frog, in reverse... :(

I tried:
disconnecting all USB/Firewire/ethernet cables.
taking out and trading the RAM
zapping the PRAM
replacing the motherboard battery and pushing the reset button
leaving it unplugged all night
trying a different outlet
trying a different surge strip
trying a different power chord
taking out ALL the hard drives.
taking out all the PCI cards (except the graphics card)

896MB RAM,  10.2.6/9.2.2

I'm stumped. Any ideas out there?? 

-Bruce Meyers