My '87 Trans Am GTA was getting hard to start. It would slowly turn over but once started everything was fine. Just installed a new battery and Alternator and now when you turn the ignition all the electrical comes on but won't turn over. When turned to ignition nothing at all happens, no noise, no slow start, it seems there's no juice going to engine or starter. All wire connection seem good.

 

Check your battery and ground cable connections for corrosion and soundness/tightness.

Barring that, rap on the starter body with a hammer. If it now starts, the starter motor is bad. Rebuild it or replace it with an AC Delco branded rebuilt.