Learn how your appliance is supposed to operate so you can determine if it is malfunctioning.
Many ranges have a clock/timer unit which can be set to control the start and stop cooking times automatically. These timer units have electrical contacts which switch power to the oven elements as need be. Those contacts can become damaged though normal wear and tear preventing oven operation. A simple visual inspection can often determine a problem with those contacts. Any signs of arcing or discoloration should have more scrutiny.
The timers can also become mistakenly set to 'auto' preventing manual oven operation. This frequently occurs when being cleaned. Check the owner's manual for how to reset the clock into manual operation.
All of the information in these Appliance Clinic procedures is provided FREE OF CHARGE. No liability is assumed by the author for the accuracy of the contents or damages caused by the use of these procedures.