While driving my car (2005 grand prix gtp) suddenly shuts off at the light then the check engine light came on then the rpm needle start moving all crazy the engine moves back and forth the headlights flicker saw black smoke from exaust, a message on the screen say reduce engine power (i appolgize for saying reduce engine tempature before) when the car did start their was power in the gas peddle now the car will not even turn on the car have under 120,000 miles if anyone have any idea what could be wrong please help