I have a '91 vert, and had her in the shop just this morning working on the top. The tops has the mechanical frame parts, the motor, the hoses, and two "cylinders" that are basically hydraulic rams that push and pull the top up and down. If the frame isn't out of whack, and it can be moved up and down manually, then it is probably the motor/hydraulic parts. If the motor is still turning and doesn't shut-down (the relay), then it is either you are out of fluid, or the cylinders are wearing out. Got leaks? Fox Resto has all of the parts here
Convertible Hydraulics - Fox Mustang Restoration
I had just had my top redone, and half of the frame replaced, and it needed to be adjusted.
Good luck.