What could cause the odometer to stop turning.

That is the #2 most common repair search for that vehicle. The answer is that testing is the only way to pinpoint the cause. Most common are the vehicle speed sensor, instrument cluster failure, and vehicle computer. Testing would help answer the question further and pinpoint the cause. Replacement of the vehicle speed sensor would be the quickest least expensive thing to try. If that doesn't work, you will need to take it to a shop for testing.