When I switched my oven on, instead of first setting the correct time, I set the 'end of programme' time and then the clock, now my oven won't heat up and I can not switch the 'end of programme' time off and back to zero. when I press the - button it does not reset it and just beeps continuously. I have tried turning the power off and back on again but it still won't help. How do I override this?