could be any number of things...but first a little clarity on the question. agitating is when the inside hub swishes back and forth to shake and move the dirt off the clothes. if it stopped during agitation, then you may have a motor or overload or drive problem. spinning is when the hub spins at a very high rate to remove as much water as possible from the unit before going to the next cycle. if it stopped during the spin cycle, there is typically a safety lockout switch that stops the spinning very quickly when the door is opened. if the switch is defective or has interference or not engaging fully then the unit will not spin. not sure about the black stuff but if unit has a belt drive, the belt may have worn out and eventually snapped.