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I have a "15" Mac Book Pro 5,1 and after running it stone dead on battery once it wouldn't power on without holding down the power button, with battery and AC removed and then plug AC back in while holding power.

This will get it in a state where it will boot but the fans are always maxed and the battery isn't recognized. If I do a standard SMC reset remove AC & battery hold power button for a while, release power and plug back AC nothing changes.

If I do the newer style leave AC & battery plugged in and hold down "left control" -option, shift and power for 5+ sec and then release power the AC light toggles like it should and then it shows that the battery starts charging according to AC light & battery test button. But nothing will make the laptop attempt to power up. I've ensured that all Software Updates are installed.

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Max fan speed at boot and unrecognizable battery presence is a sign that the SMC reset has been done incorrectly – AMomchilov Feb 26 '12 at 1:06

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