weird retraction issue

hello,

had a break from 3d printing coming back to it, not changed any values in skeinforge or marlin(except for making sure the z height was correct). now it seems as if when printing, it retracts but doesnt unretract to the same point so the first outline comes out but then it retracts and the filament doesnt get extruded it does it repeatedly so it knocks on to the point where the filament comes off of the hobbed bolt.

any suggestions would be greatly appreciated, about to print a previously sliced object and see if it prints ok

as i said i just tried printing a previously sliced object same issue so it must be a printer issue so if anyone has come across it id love to hear about it.

proof that i have learnt something, turns out the stepper motor potentiometer some how changed the value once re calibrated the value seemed to have sorted the issue.