WLAN on laptops is not on mobile phones and Smart TV, what is it?

Hi, on our two laptops suddenly our wireless router is no longer displayed (means: in the list of possibilities of connections, the domestic Wi-Fi is no longer displayed). The one laptop has been in the house for years and has always been connected to the internet here, the other for half a year too.

On the smartphones, the Smart TV and the switch of the house, but all goes without any problems - what is it?

Look at the Lepptob if there's somewhere (front most) a switch (slider) or above the Tastartur a button there for