Hi @blute,
open a terminal with Ctrl + Alt + t and paste the following command:
sudo apt-get update && sudo apt-get install broadcom-sta-dkms
and see if that fixes the problem for you!. 
Or, install the binary package from here:
https://pkgs.org/ubuntu-16.04/ubuntu-multiverse-i386/broadcom-sta-dkms_6.30.223.271-2_all.deb.html
according to this:
https://zareason.com/shop/Alto-X445.html
your laptop is supported out of the box?.
Is your Wifi switched off on the keyboard?. Is WiFi enabled in the network manager icon in the top panel?.
Have you done a full system update using a cable connection?: