MacBook won't wake up from Hibernation

I have a MacBook that won't wake up from hibernation mode.

i wanted to drain the battery and let the MacBook go all the way down.

(i needed some voltage informations from the "empty" battery)

removed the battery, made my "stuff" and tried to start the MacBook again - but nothing - it stays dead, i charged the battery in another MacBook, put it in the dead one and nothing.

tried to start it with the powercord & the battery, only with the powercord - but still nothing.

tried it without the topcase (to rule a topcase problem out)

it does not react in any way.

changed the dc-in board - nothing.

one thing i noticed - the magsafe connector does not show anything when plugged to the MacBook (tried several ones) - BUT, when i plug in the magsafe and press the power button, the magsafe connector starts to flash orange (very faint)

any suggestions what in could try ?