Car won't start airbag light is on.

Hello, the air bag light will come on as a normal "prove out" of the restraint system when the key is on and the engine is off. Do not concern yourself with this. If the vehicle will not start, begin by having the battery checked for the ability to hold a load and state of charge. Once you eliminate this possible variable is being the cause, then you can move on to other areas of concern. But the battery is the most likely cause of the problem here.