Ultrasonic sensor controlling DC motor

Looking at your wiring diagram I would not expect it to work. You need to power the motor with an external power supply. By connecting the motor to the Arduino you could have possibly damaged the Arduino. Here are some simple rules to follow:
Gil's Crispy Critter Rules, they apply to processor hardware:
Rule #1. A Power Supply the Arduino is NOT!
Rule #2. Never Connect Anything Inductive to an Arduino!
Rule #3 Don't connecting or disconnecting wires with power on.
Rule #4 Do not apply power to any pin unless you know what you are doing.
LaryD's Corollarys
Coro #1 when first starting out, add a 220R resistor in series with both Input and Output pins.
Coro #2 buy a DMM (Digital Multi-meter) to measure voltages, currents and resistance.
Violating these rules tends to make crispy critters out of Arduinos.

Do another schematic following the above rules.