1- Check the fuse on the motor. It is possible that you reversed the leads to the battery and blew the fuse.
2- Check that the battery is good.
3- Clean your battery posts and clean the connectors on the end of the battery cables..
4- Tighten the connections on the battery - wrench tight.
Having to remove and connect the battery cables to start the motor... point me to the connections at the battery, the battery, or the battery cables themselves.
If #1 - #4 do not get it going...check for and watch the voltage at the points where the battery cables connect to the engine itself. Check the connections and watch what happens to the voltage at those two points when you try to start the motor. It should dip down some but not go away.
If you have good voltage there and there is no clicking, then check all the connections to the voltage regulator. That is where the starter solinoid gets its voltage to operate off of the switch.
Let's see what you get to that point.
Mike