rotate the axes in manual mode

Hi, i have a prusa I3 pro B machine.
I try to rotate the stepper in manual mode (using the menu in the lcd..prepare-->move axis-->move 1mm) and i discover that only the extruder axis doesnt work.
The stepper is ok because i change connection of axis x to extruder axis, and it rotate..but if i reconect the stepper of extruder to his cable, nothing append.
The printer is new, and i dont know how is the problem...
Is it possible, changing firmware to change the main extruder to second one?
Thanks
Matteo