L298 Motor Driver not showing Red light when connecting power supply
You need to do math on the power consumption as arduino uno takes takes 5 V 500 mA at least for it to work. That is why it can be powered by USB cables too.
Now if you try calculating power consumption on the motors you would understand that the power you are giving is nowhere enough for the arrangement to work or you could have been able to run the motors without the motor driver.
Try upgrading the power you are giving.