Changed alternator now car wont turn over or start

Unless your battery was discharged from old alternator,that's impossible and the battery will have to be charged with a battery charger! the battery/starter is what cranks the engine over,unless something shorted during alternator swap out,like not disconnecting the battery terminals before removing the hot wire on the alternator.Test all fuses with a test light.how many volts at the battery terminals,testing with a volt meter?