If you had it hooked right + to + and - to -.
Then what you have done is telling me that you have ONE of just a few problems
Bad Starter motor.
Bad Ground cable from Battery to frame (or bad terminal end or dirty connector).
Bad cable from battery to solenoid.
Bad cable That is hooked to the starter.
Or a FROZEN up engine (which I doubt because you said it would start if you hooked the charger up to it..
But, if the unit would start if you hooked the charger up, how did you have the charger hooked up.
From what to what.
So, if a different battery did not help
and if the charger will start it
then we are saying the starter it good.
So the only thing tis leaves is a bad cable or a bad ground..
By jumpering the two large solenoid posts together, we have bypassed the starter solenoid, so it only leaves the cables or the ground (which is still cable related).