Any hope of recovery from a deep coma?

My 15-inch Core 2 Duo MacBook Pro (model A1260) will power up but is otherwise comatose. Pressing the power button yields the usual noise from the optical drive, and the hard drive spins up, but then nothing further happens. In particular, there are no sounds from the hard drive suggesting any head movement. Screen is dark and blank (I've checked that it's not just a failed backlight); no response to mouse or keyboard (not even the caps lock light); the machine cannot be reached via wifi or Ethernet or Firewire; it does not mount external drives. Won't boot from the original Apple DVD.

My first thought was a power problem, but in fact that seems to be the one subsystem that's working normally. I can get green and orange lights on the magsafe connector; the battery charges and discharges.

I've replaced the hard drive with a formatted backup; no change. (The drive I removed works fine with another machine.) I've tried swapping RAM, again with no change.

Do these symptoms ring a bell for anyone else? I have a sinking feeling it's going to take a new logic board, and I'm not sure the machine is worth that investment.