The firmware has a safety feature that stops the extruder from moving if the nozzle temperature is lower than a certain value. This will prevent the extruder from pushing filament while the nozzle is cold.
So, before you can turn the extruder motor, you need to raise the nozzle temperature above 180 degrees C.
If the motor still does not turn after the nozzle is above 180 degrees C, check the motor cable.
For troubleshooting, you can swap the cable from the extruder with the X axis for example and test. You can also swap the drivers (make sure you have the power off when you do this). This will allow you to check if you have a problem with the motor itself, the cable or the driver.