Hello, thanks for the message.
Just to be clear, there are no jumpers involved for motors. Be certain that you are only plugging in motors to the two motor ports on the side of the Bricktronics Shield by the Arduino's USB and power ports:
The only jumpers needed are for sensor ports 3 and 4, which support a variety of sensors.
What are you using for a power supply?
What kind of LEGO motors are you using? The standard NXT "servo" motor?
When you run the MotorSingleBricktronicsShield example code, what do you see for serial printouts? That example code will drive the motor forward slow, then forward fast, then reverse slow, then reverse fast, then repeat. Does the motor move at all after it prints out "Going in reverse." ?