Liz,
We won’t be able to offer any specific advice without the model number.
Basic principles would suggest:
1) Ensure cooker timer set to manual
2) Selector switch may be faulty.
3) Safety thermostat may have been tripped.
The last two options require test equipment, if you can’t do this safely, send for an engineer. You can check in the Directories section for a UKW engineer in your area, or pop up your postcode in here and someone will pick up on it.
Don’t wait too long, it’s starting to get tight to order parts in time for Christmas.
Regards,
Penguin45.