general problems of the 2009 Nissan Altima

I was in a parking lot, about to leave from plasma center. Entered vehicle and attempted to start up. Would not start. Looked up warnings of key symbol and car symbol. Referenced to steering lock failure. Was never able to get vehicle cranked. Numbed var battery and changed battery in fob. Still nothing. Had vehicle towed home. Contact end Nissan who stated warranty is out. Please help.

While driving down route 1 in norwood, MA. My dashboard panel went dark and my engine shut off. I was driving approximately 40 mph. I was able to coast to a stop, put the car in park and restart the engine. The engine did not sputter, or present any issue prior to the shut down. I took the car to the dealer and they said there was nothing wrong with the car. This leaves me feeling very uncomfortable as with no root cause identified it could happen again in a heavier traffic situation. Besides my own safety, I am concerned for other Altima owners.