If your oven suddenly won't heat up, before calling a serviceman or electrician, or purchasing a new element, it is wise to check the state of the clock timer. Most newer ovens with a digital clock won't work unless the clock is set. This can happen if the power goes off. Some, such as Chef, are kind enough to spell out HELP. Others just go blank. The procedure for resetting the clock varies, so you should consult your manual.
On older stoves & ovens with a mechanical clock timer, it is common for the start & stop buttons to get bumped when cleaning and the timer switches to Auto mode. In this case the oven won't go if turned on at the thermostat. To reset this you need to turn the start knob around until it clicks, then push the stop knob in to put the timer in manual mode.
This can save an expensive, unnecessary service callout fee, or wasting money on an unneeded part..