Network Manager stops working after an update to ca-certificates
You may as well try to run this command from the terminal as this worked for me:
sudo apt-get install --reinstall libnss3:i386 libnss3
I'm not sure what you have tried, but you could run nm-applet from the run dialogue, and it should start your networking icon. If it does not start, run:
sudo start network-manager
nm-applet & disown
In a terminal.
Edit: Jorge pointed you to the right place.