Check for hair or fuzz or other foreign matter wrapped around shafts and gears. If you fly inside this is likley the issue.
If all that seems clear and the one rotor turns then you know it's not the battery. So can you hear the motor trying to turn the blades ? On coax heli's there are two motors, one for each rotor. If it is then something jammed. If you hear it running (both motors) but only one rotor is turning then something is disconnected in the drive train, stripped a gear, etc. If only one motor is doing anything you can swap motor leads and see what happens- if the same motor turns as before then the one motor is bad or the problem is in the gearing/shaft for that motor. If the 'bad' motor' now turns the 'good' one doesn't then it's your controler that is bad.