Eliminate the simple explanations first:

1. No electrical power. Today, most gas ovens require electrical power before they will operate. Confirm power by checking the breaker box, observing the indicator lights and/or testing the supply outlet.

2. Make absolutely certain that the controls are set correctly. This is particularly true on all self-cleaning models.

3. Carefully check all clock dials that control delay cooking and self-cleaning time. On many brands small pointers that set time accidentally get depressed and disable the oven. Be positive that the oven is set on manual operation. Pay close attention to the "Push for manual" button.

4. On electric models, visually check the faulty bake or broil element for flaws. Almost all bad electric elements have a bubble, wrinkle or hole where the heating element has burned out. Replace the element as needed. Elements are different for every model and require model numbers for ordering.

5. A few modern ovens also have internal gas pet cocks controlling bake and broil gas flow.

6. Many older models utilize a standing pilot for gas ignition. Check that the pilot light is lit. Ash often builds up around the pilot orifice and restricts the flow of gas. A sharp rap on the pilot housing will usually free the obstruction.

If these six suggestions don't locate the problem, more detailed diagnosis is needed. Please consult Manual 11: Ranges, Cooktops and Ovens.