If a Light and Darkness Dragon exists on the field and Geartown is activated, Geartown's activation will be negated by Light and Darkness Dragon and Geartown will be sent to the grave by game mechanics.
Geartown will summon nothing from the main deck/hand/graveyard because its requirements were not met, it wasn't destroyed. It was just sent to the grave.
Geartown will summon nothing from the main deck/hand/graveyard because its requirements were not met, it wasn't destroyed. It was just sent to the grave.