There you go you waited to long between dead battery and reinstall of the new battery the NATS nissan immobilizer system has energized. (flashing red symbol of a car with key inside) The car body control module has erased the memory of the keys and is in lock mode. Gather up ALL THE KEYS and remotes tow the car to the Dealership there they will re introduce your keys for a price generally around a one hour minimum service charge. Good Luck