Solution 1: Perhaps the rechargeable batteries of the parent unit are empty and the parent unit is not connected to the mains. Insert the small appliance plug into the parent unit and put the adapter in a wall socket. Then press the on/off button to establish connection with the baby unit.
Solution 2: Perhaps the non-rechargeable batteries of the baby unit are empty and the baby unit is not connected to the mains. Replace the non-rechargeable batteries or connect the baby unit to the mains. Then press the on/off button to establish connection with the parent unit.
Solution 3: The baby unit and the parent unit may be out of range of each other. Move the parent unit closer to the baby unit, but not closer than 1 meter/3 feet.
Solution 4: If the LINK light on the parent unit still does not start to flash, use the reset function to reset the units to their default settings.