Some symtoms of a dead logic board are as follows:
Drives spinning up
nothing displayed on the screen
no power throught USB (or the otherway around)
No Power Through firewire (or the otherway around)
fans running at max speed
computer heating up abnormally
display image distortion (prior to fail)
So if my MBP isn't showing any response when I hit the power button... no light, no fan, no optical drive activity, no HDD activity, no screen activity, no chime...
What might this be? Doesn't matter what the power source is, same response with battery and AC. I thought it was a bad logic board, but this makes me hope otherwise.