I was able to fix it a little
I had the same problem.
Completely dead MacBook Pro 15" 2008
removed power
removed battery
held power key for 5 seconds
continued holding while putting power cable back in
released power button
pressed power button
Fan comes on at high speed, black screen, no response to input
Did the steps above again, but immediately zapped the PRAM (option-cmd-P-R) after the last step
Startup chimes sounded (once)
Same result except now the screen was gray instead of black
Ran through the steps again, again zapping the PRAM until I heard the chimes twice
It now is on the login screen - so it seems to have worked.
The battery icon shows an X, and though the power cable is plugged in, the cable's light is not on.
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Shut down and waited 2 hours. Power cable still plugged in. Battery still out.
Pressed the power button. Computer came on and back to the login screen. Logged in.
Seems normal, except the fan is still going strong. The power cable light is still out.
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Shut down and reinstalled the battery. Cable still connected.
Pressed the power button. No change from before. Computer came on. Power cable light still off. Battery X'ed out - as if it was not installed.
I probably need a new battery.