Something was damaged in that nose-over landing. Either one of the windings is broken in the motor, or one of the phases in the ESC is burned out.

Did you land with power on? A common newbie mistake is to forget to shut the throttle off when the plane noses in. Leaving it sitting there with the motor in the stalled state for any length of time can cause burned windings or ESCs, even with Castle's overcurrent protection.

How hard was this landing, really? No offense, but some people's idea of a "nose over" is actually a "lawn dart."