There's no network menu in the menu bar
If the network menu has disappeared from the menu bar, your Network Manager may not be running. To start it up again:
Press Alt+F2
Type nm-applet and press Enter.
The Wireless Network Authentication box may pop up. Enter your password in the appropriate box and click Connect.
If this doesn't work, there could be a problem with the Network Manager. To see if this is the case, go to the dash and open the Terminal. Type nm-applet and press Enter and see if the network menu appears. If it doesn't, you should see some error messages appear in the Terminal. These should tell you what is going wrong, but they may be quite technical in nature. If so, ask for help on a support forum and quote these error messages.