Thank you David..
Behind the front panel of your dishwasher there is the rear of your dispenser.. on that dispenser is a solenoid which actuates the door of the dispenser.. Either the solenoid has stopped working, the actuating mechanism is broken, or the pcb has stopped giving power to the solenoid.
The solenoid is available to purchase as a separate part.
I ask that you now rate the assistance given, following which, further advice can be given if needed.