I have 2 motors connected to a dual H-Bridge motor driver and the H-bridge connected to an arduino uno, It was working fine at first but now my motors are spinning very slow and the car bearly moves, I have changed the batteries but still moves slow and with no power, please help
You can try to bisect the problem.
Remove the Arduino and drive the motors with wires: replace the input for the pwm signal with a +Vcc and you will get the same as if the Arduino was outputting a PWM with 100% duty cycle.
This should allow you to diagnose if there is a problem with the driver/motors.
If that shows no problem and the wheels spin as expected, then you have some issue (either sw or electrical with the Arduino).
But at least you can halve the complexity of the problem.