serifos

Hello, I just finished assembling my new Ultimaker, but I have a problem with the extruder motor- it is only moving back and forth in small steps? After I have heated the extruder, I have tried to extrude something using Cura but when you send the command the motor just moves back and forth? Any ideas on how I can resolve this? Is it possible that there is a problem with my board? Thanks. Brian