This probably holds also for other Lenovo Thinkpads.
Machine won't boot. Nothing seems to bring it back to life. Brick state.
There is a small hole on the backside of the laptop. In T450 it's roughly at the other side of the touchpad. There is no text or symbol next to the hole.
You need to press the magic button in the hole.
This apparently resets something related to battery state.
You need have a correct combination of: