I was flying and all of a sudden my tail rotor stop spinning I changed the motor and still no spin I checked the polarity and no spin I checked the motor on the power supply and it spins. What would be next?

If the main rotor IS working then it could be a problem with the 3 in 1 board (tail ESC), the connection to the motor, a Rx connection problem.

If you're sure the tail motor and capacitor is good (it works with a different power source, etc.) then work back to the 3 in 1 and verify all connections.

Swap the motor connectors, i.e. the tail plug in the main motor slot and vice versa, and power up SLOWLY. If the tail motor spins and the main doesn't, you need a 3n1.