Hiya,
You need to check a few things here.
You'll have to take the door apart, careful of sharp edges.
First, unplug the appliance from the wall socket.
Open the door and remove the screws holding on the facia and outer door panel.
Once you've done that, examine closely the pcb and door switch.
Use a multimeter to test for continuity on the on/off switch and check for broken connections.
If everything up top of the door looks good, examine the wiring especially where it goes under the door and into the base, you may have to open the protective sheath. You're looking for cut or broken wires.
If still having problems, post the model and product number of the appliance and I'll dig deeper into your fault.
Good luck with finding the fault.
Thanks
Home Appliance Technician
Whitegoods engineer working for a multibranded national company in the UK.