My 2002 Yukon will not turn over

Make sure battery has a full charge and connections all good. If your saying it cranks good but won't start, Have a helper crank it while you check the basics, spark--proper fuel pressure and fuel injector pulse. Any applicable trouble codes? Now, if your saying the starter motor won't crank the engine, that is a different issue. Have to check starter motor wiring circuits, voltage and ground. The diagram 02 Yukon, 5.3L starter wiring diagram