Thank you for your question. Do you hear the motor running? if not remove the B pillar trim and check power to the motoer with a test light. If you have power you will need a new motor. If the motor runs but it doesn't move you will prbably need a new track and belt assembly. Below are instructions to temeraliy drive the car until it is repaired.
If the shoulder belt does not move or stops before reaching the B-pillar position, perform the following steps before driving the vehicle:
Important: If the shoulder belt will not move forward to the A-pillar position, press the red emergency release button on the buckle to exit the vehicle. Then check to see if the Inertia Fuel Shutoff (IFS) switch has been tripped.NOTE : The inertia fuel shutoff switch shuts off power to the fuel pump and the passive restraint system.
There should be a pink and yellow wire and a black and white wire in a connector near the motor in the b-pillar. One of these should have power depending on which direction the motor is being commanded to turn. Here is a wiring diagram if it helps.