2009 Cadillac DTS. Filled car with gas. Next morning car would not start. Replac

Without personal *hands-on* testing - ALL we can offer here 'online' is a guess. One *possibility* is there is an EVAP problem causing the engine to flood after fuel tank fill up. Try HOLDING accelerator pedal to floor while cranking engine. Highly recommend contacting local auto repair facility to discuss repair arrangements. NEVER 'top off' fuel tank when refueling!