Are dishes, utensils or dishwasher racks blocking the dispenser that kept it from opening?
Items blocking the detergent dispenser will keep it from opening. Load items in the lower rack as directed in the Use and Care Manual to avoid the dispenser door being blocked closed. Make sure water action can reach the dispenser.
Is the detergent old (when using powdered detergent)?
Older detergent, exposed to air, will clump and not dissolve well, which causes the dispenser door to stick to the detergent. Replace detergent if necessary.