Car will not crank

I have a 2006 Pontiac Grand Prix and the headlights would not come on so when I got the car checked at the parts store I was told that the battery was functioning at 0%.  I purchased a new battery and then I had to get a starter.  Now the car still will not crank and the headlights will not come on.  I also tried to see if the car had gone into sleep mode.  What are your suggestions for my next step?