my 04 cavalier wont start and has no power

I have a 2004 cavalier ls, and it jus wont start, it does kinda start but theres no power, i mean i have one of those loud mufflers on 2 but when it starts it just sounds like a stock vehicle, and we changed da fuel pump, fuel filter, got another fuel pressure regulator, got n new coil and a new module 2 and it still wont start, i need help!!!! PLEASE, WHAT COULD IT BE? :frown::frown::frown::frown::frown:

Check the crankshaft position sensor.