Pontiac won't start just click drove yesterday

Sounds like something you did either drained your battery due to a wiring issue or something left on in the car like an accessory or lamp or the alternator is not providing a solid charge to the battery due to a defective unit or, possibly, a loose belt after installation. Check 'em out and see what you find. I am assuming the battery was good/new that you put in.

I first would see if the lights come on at all. Even if they glow a little. if they don't come on at all and there are no dome lights etc that means there is no connection. Either from the battery or possibly to the alternator. Disconnect the battery cables from the battery and reconnect them. They could be loose.