Ensure that both of your belts are attached correctly. Each belt should wrap around two pulleys and be taut.
Check motor direction settings
Under Home > Setup > Updates, Look for the button that says Motor Forward or Motor Reversed. The text on the button indicates the current direction of the motor. Be sure that the Motor direction button reads Motor Forward. If not, change it from Motor Reversed to Motor Forward.
Set Variables to default
Under Home > Setup > Advanced, Factory Defaults.