Ok. Best to post only in one place for assistance however i understand why you may now feel this isn't a firmware problem (not a soft-bricking) so we'll continue here for the present to hopefully rule out a hardware fault or hard-bricking. If there is no sign of the device powering on at all then soft solutions such as using cure fw can't be used.

Please let us know the results of testing 1 - 3 as per Post #2 then we can see if it's a (feasibly) fixable problem.