check and make sure the takeup spool is turning while the tape is moving, and if you took the mech off the board, make sure the pin on the mode switch is properly aligned with the hole in the mode switching wheel on the bottom of the mech. a lot of times the pin gets broken off the mode switch, so this can cause problems.
also, some takeup spools use a belt to a wheel with some kind of sensor. if the belt is loose or missing, the vcr stops to avoid eating tapes. so if the takeup spool is actually moving, check for a belt or some type of friction wheel connecting to a wheel with a hall sensor or opto sensor. if the capstan and pinch roller aren't moving, check the long belt under the mech.
most vcr mechs made from the late 90's onward are extremely similar with a few variations.