This can have several causes:
My Philips SmartPro Active robot vacuum will not switch on
Cause: The rechargeable battery has run down
Solution: Charge the rechargeable battery. Detailed instructions are in the article 'Charging the SmartPro Active'.
Cause: The on/off switch is not set to 'on' (I)
Solution: Make sure the on/off switch on the side of the robot is set to on (“I”) and the robot is connected to the charger or plugged into the docking station. After a few seconds a charging light will light up on the on/off button on top of the robot when successfully connected.
Cause: The small plug is still inserted in the socket on the robot
Solution: The robot does not work on mains power. It only works on its rechargeable battery. Therefore, always disconnect the adapter from the robot and the mains before use.