take a close look at the tensil leads on the speaker. the tensil leads are the wires from the speaker terminals to the speaker cone. I have seen these leads close to or actually touching the speaker frame and this has caused speakers to not work. if the leads are ok, try putting opposite pressures on opposite sides of the speaker. in other words push slightly down on one side and slightly up ( kinda tweaking) on the other side ( don't press toooo hard). what your testing here is to see if
the speaker cone is locking up.
a ? here, when you start to screw the speaker in doyou see a slight spark?