Creality Ender 4 extruder problem
Apparently your 3D printer runs Marlin firmware. Marlin firmware default code has build in protection against extrusion below a certain temperature (usually 170°C) as defined in the printer configuration:

// *** IT IS HIGHLY RECOMMENDED TO LEAVE THIS OPTION ENABLED! ***
#define PREVENT_COLD_EXTRUSION
#define EXTRUDE_MINTEMP 170 


Are you sure that it heats up above this temperature? Please check the connections of the thermistor and the heater cartridge.

Marlin firmware code supports disabling the cold extrusion safety measure by setting:

M302 S0    ; Allow extrusion at any temperature


(save this line in a file with extension gcode and load and run it from an SD card or alternatively hook up your computer over USB to the printer and use an application like Pronterface, Repetier-Host, etc. to upload the command to the printer)

If cold extrusion safety is turned off, you should try to extrude (without loading filament) to test if the extruder works.

To revert use the following code:

M302 S170  ; Allow extrusion above 170