Hi, I assume the model is a Rotak 32-12.
The most likely cause will be a blown fuse in the lawn mower plug.
If you confident the extension lead and plug socket your plugged into is working, by testing it with a lamp or some other mains device, the fault is with the mower.
If you have changed the fuse in the plug and still have the same issue, I would look to take it back to the store and arrange a replacement as its most likely a faulty switch or motor, as there are no other reset buttons of controls which would cause this fault.
Please let me know if you require any other assistance.