It sounds like one of two possibilities...

- One: And the most likely... one of the three wires to the brushless motor from the ESC has become disconnected.

Check to see that all three are plugged in.


- TWO: You may be turning on the plane with the transmitter on, but in the wrong throttle position. This prevents the ESC from learning the stick movement range of the throttle, causing the problem you are seeing... OR... the programming of the ESC is currently wrong for your motor.

I would look to the wires first though...