extruder motor not working

Hello, I am new here, I hope I put this in the right spot.
I have A mendelmax with ramps1.4 electronics and arduino 2560 ,and Marlin firmware..
I cannot get the extruder motor to run,I it runs fine when i plugged it into another set of axis pins,so it is not the motor itself.
The other axis motors run fine,however the y axis seems to "overstep",being that when I jog it 10 mm it advaces a little more than. 20 mm.
Which i wil have to change in the fimware when I get to that point,and get that figured out.
The question I have do you think the board is bad or maybe it needs to be turned on in the firmware?

While I am asking questions how do I get the firmware into the arduino editor,what file do I need to look for?

Thanks,
David