If you change the settings of your network connection or connect to a different network than usual, you may have to enable the connection yourself.
If your network connection is managed by Network Manager (as most are), the connection should be enabled automatically.
If the connection is not enabled automatically:
Find the Network Manager icon in the notification area. It should look like a small signal strength indicator or a computer monitor and will probably be close to the clock
Right-click the icon and ensure that Enable Networking is ticked
If you have a wireless network connection, also ensure that Enable Wireless is ticked
Left-click once on the Network Manager icon and then click on the network you want to connect to
After a short period you should receive a message which says Connection Established
You should now be connected to a network.
If you are not connected to a network after following the procedure above:
Left-click the Network Manager icon again and press Manual configuration...
Select the Connections tab
Tick the box next to your network connection to enable the connection
The connection process make take a short while
Press Close
ifup is a command-line tool for enabling network connections.
To enable a network connection:
Press ->-> to open a Terminal
Type sudo ifdown eth1 in the Terminal and press Return, replacing eth1 with the name of your network interface if it is different
Enter your password if prompted
Type sudo ifup eth1 in the Terminal and press Return, again replacing eth1 with the name of your network interface
If you have connected successfully, you should see a message similar to the following (the numbers may be different):
DHCPACK from 192.168.2.1 bound to 192.168.2.4 -- renewal in 536349522 seconds.