When you turn on the oven and one or all burners turn on and then shut back off could be two things. First is the oven already at set point? If so the burners will cycle on and off to regulate the temperature. If it is just being started in the morning or not at set point, then you will need to check the igniter for the burners under the oven. If the flame sensor that is attached to the igniter is fouled or has carbon build up it will not read the flame properly and shut the valve down for safety. This can easily be fixed by cleaning off the igniter with a scrub pad or steel wool. Cleaning off the tri-electrode (igniter) every other week or monthly will prevent this from happening in the future.