CODE P0300 2004 infinity G35 Coupe?

I have a 2004 infinity G35 Coupe. Took it to autozone and it generated Code p0300. Car does not run, when It turns on the engine starts thumping almost making the car shake. I've changed all 6 spark plugs, front and rear camshafts, and the mass airflow meter. I keep having the same problem, nothing seems to work. PLEASE HELP!