03 Santa Fe car sometimes won't start but only when immobilizer light stays on will start after a while has power just wount start

Yes. Immobilizer lamps that stay on or continue flashing indicate the vehicles immobilizer has not recognized a valid key. Depending on the system, the vehicle may start with a correct rotation but invalid key, or it may not crank. Your problem us most likely a defective key, however the immobilizer antenna could also be weak and not properly picking up the key. Both problems will require a dealer or technician or locksmith with special tools to learn new keys to your immobilizer.