It won't turn over no ignition after replacing alternator

If your saying the starter motor won't crank the engine, you have to sure the battery has a full charge and battery cables/connections all good. That means using a digital multimeter across battery posts, everything off, take a reading. The generic spec for a full charge is 12.6 volts. If battery is down, get it charged. You can't do any testing if battery is down. Did you try jumper cables or jump box to see if starter would crank? Another thought, if you disconnected battery to replace generator, it might have activated your security system, where applicable? If security system is involved, I doubt I can help you from here?