I wonder, you say the engine is not turning over, does it make any noise at all? Does it sound like a weak roll over (RrrrrrrrRRRrrrrr like a dead remote control car on it's last legs trying to move) or does it make a clicking sound? Does it make no sound at all? Do the chimes inside work? (Door Dinger, etc) Or overhead dome lamps? Do your new headlights work when installed? If all this is working and your car is not trying to turn over, then check your electricals to your starter. If it makes no noise that means that the starter is not spinning the crank, and that's the problem. If it's making a weak noise, then your battery for some reason is not strong enough to spin the starter at full speed, and if it's making a clicking noise...well your starter might be out of position on the crank. Some more info about what exactly the issue is would be helpful, unless you already got someone to figure it out for ya.

Hope I can help, and Merry Christmas.