Which display specifically is it? A PanelDue? Which one?
When you say blank, do you mean a white screen or nothing at all? Photo?
What firmware version on the Duet? How is it wired to the Duet?
Have you tried flashing the firmware on the Paneldue?
When you say you replaced it with a new display, what exactly did you replace? the LCD itself or the entire Paneldue? Assuming you mean paneldue in the first place.