If you have a new Wi-Fi router you probably also have a new Wi-Fi name and password.  Since the cameras only have the old Wi-Fi information, they cannot connect to the new Wi-Fi.  To fix this issue, you must reset your camera using the reset button on the camera.  This will reset the camera back to factory defaults.  You will also need to delete the cameras from the SightHD app on your phone.  From there you just need to set the cameras up again as if they were new.