[tsac]

Welcome to the forum.

You said the battery was good and checked in the same BB. How did you check it? If the BB wont start them the first item most check is the battery. Next is damage. Was it wet or dropped? If it was dropped them it could be a physical problem on the electronics. If it was wet then the power connections could be corroded and not allowing the battery power to feed the phone.
I would try the battery in another phone of the same type.
also try to check the connector to see if it has any corrosion, dirt or bent pins.

Repost if you figure this out