So you know the starter turns over when given 12v, and you know the starter won't turn the motor over. Maybe step back, you could be getting burned out.
If you can hear the starter engage when you turn the key and everything is hooked up, something is keeping the motor from turning over. If you can't hear the starter engage, replace starter. It's not unusual for replacement starters to be junk, depending on exactly what you bought.
Stick a breaker bar on the crank bolt and see if she turns over.