If the burners on your gas grill don't get gas, first, check the tank's propane level to make sure the tank has gas. Next, reset the pressure regulator to restore gas flow through the regulator if the regulator's flow-limiting device tripped. Replace the pressure regulator if it doesn't allow gas to flow to the manifold after resetting the flow-limiting device. Check the operation of the burner valves on the manifold and replace the manifold if gas doesn't flow properly to the burner tubes when you open the manifold's valves.
Gas won't flow through misaligned burner tubes, so check and adjust burner tube alignment with the gas valves. Clogs in the burner tubes can also inhibit gas flow through the tubes. Clean clogs such as spider webs and spills from the burner tubes to restore gas flow through the tubes.