Oven has power, preheat light is off, but no heat
Electric ovens use heating elements to create heat.  These are prone to "wear out" over a long period of time.  The typical way that these fail is by going open (meaning no heat produced).  This website (https://www.partselect.com/Range-Stove-Oven+Baking-Element-Testing+repair.htm) has good information on how to test and replace the element(s).

I suspect the problem with your top broiler might be a wore out element as well.  Might as well check them both while you are looking at it.