I'm following the help files to get networking up on a new system. I'm very green with Linux. I've configured "Networking" for my wireless and ethernet cable, assigned a proper IP address and the wireless connection finds my wireless name. Both services have a check mark in Network Settings. But a ping to my router fails and Firefox is not connected to the net.

What am I missing?

try to reset your router, it works for me

Go to a shell. Run, as root,
If that fails to start the network, then, as root, do:
and paste the results here.

Others will have a much easier time helping you if you can work in a shell. There are too many different GUIs and GUI applications for anyone to know what you are referring to. Using a shell, you can paste the exact results of your diagnostic into this forum, and you can receive instruction with commandlines that people can write directly.

--- rod.

Sorry to be so green. By shell do you mean Terminal? And if so, do I enter the following after the prompt? /sbin/ifup eth0

Or must it be preceded by "sudo" (I told you I was green...)

Well, a terminal can mean many things. Generally, any tool that gives you a commandline is running a shell. You could also go to a text mode console, or boot to runlevel 3. For this purpose, it doesn't matter, except that running in a desktop probably means you can use it's copy & paste functionality to post results here.
Running as root can be done either with sudo, if it is so configured, or by logging in as the root user, or by running a single command as root:
This method should be universally available, I believe. Again, for this purpose, it doesn't matter which you choose, as long as you get root privileges.
--- rod.

/sbin/ifup eth0 returns the message "interface eth0 already configured", but it seems to have unblocked it. I can now access the net and see shared devices. Thanks.

I tried to share a folder from Ubuntu and am told "Sharing service is not installed". I tried to install service and get a "not found" error (404) on the file name, which is:

http://us.archive.ubuntu.com/ubuntu/...tu4.7_i386.deb

There is a very similar file at this location for "lubuntu4.9" instead of "lubuntu4.7". Should I, and is there a way to, manually install this file?

The 'sharing service' falls under the umbrella name 'samba'. Most modern Linux distributions include both a samba client and server. The server component can be tricky to set up. To start it, you probably want to do, as root,
That will probably do nothing for you, because you need to configure the server by appropriately editing /etc/samba/smb.conf (may differ on various distros). Once you've done that, you can restart the service:
Prepare for numerous iterations until you get it right.

--- rod.

@theNbomr,

Just so you know, by default, Ubuntu has the root account locked, so users can't su to it. The prescribed Ubuntu method is to sudo (or gtksudo) commands that need to run as root. Members of the admin group can sudo any command from their own password. On a default installation, the user account set up at installation is a member of admin.

Also, the default installation of Ubuntu includes the Samba client but not the Samba server. The server is available from the repositories.