Capacitors store up electric current and transfer it to your washing machine's motor to help the latter start up more easily. They also help maintain the torque. Clearly capacitors are the lifeblood of the motor!
If the capacitor is defective, the motor will attempt to start but will be unable to.
It may be that the capacitor heats up, starts leaking or inflates. If you are encountering any of these issues, you need to replace it.
Find the right capacitor for your model on this site!