Engine doesn't turn over. Battery isn't dead

Hello, Perception of the battery not being "dead" could be slightly misleading. A different amount of power is needed to turn lights on, compared to the power needed to turn the starter motor which turns the engine to start it. Start with a battery test first. A good tester will check state of charge and the ability to handle a load. Once you eliminate the battery and find it to be officially "good", you can pursue further testing of the electrical and engine mechanical systems.