I did a double check on all the wirings and it looks correct (as per the easydriver tutorial and above figure). Still getting the vibrations on the stepper, no turns. :~
Edit: I set the delay at 100 microseconds and at least it started turning again. However the stepper is behaving erratically i.e. when a little resistance is applied it changes direction (video below)!
I would think this should not be its normal behavior.