I'm in the process of cleaning up a laptop to be given to a son's family. Since I had xubuntu 8.04 installed on it, via wubi, I decided to do some experimenting before wiping the wubi install completely off the disk, so I did a version upgrade to 10.04. My main purpose in this is simply to gain experience in an area I had not previously touched; my other version upgrades were all clean installs, and this is the only machine of mine that's used wubi.
That upgrade went fairly well, but since the wireless chip in the laptop is a Broadcomm I had a bit of trouble getting the box back on line before discovering that 10.04 included the necessary drivers under "Hardware Drivers." By that time I had rigged a patch cord from my LAN switch to the laptop and for a while had both eth0 and wlan0 working at the same time.
Emboldened by that, I then did another version upgrade, to 12.04. It completed, but on the reboot at the end of the upgrade, /dev/sdb1 (my /host partition) failed to mount because it was already mounted for exclusive access. I hit S to skip it for the time being, and the system then began waiting for network configuration. It never finished. Eventually it continued without full network capability.
Once I was logged in, I checked "ifconfig" and both interfaces reported they were up and running. I can ping another box on my LAN, presumably via eth0, but only by its IP address. Apparently no DNS server is working on this installation. I've seen posts about dnsmasq but have not yet found how to deal with it, if that's the problem.
At this point my question for this forum is simply "How can I get networking going again?" It may be relevant that there's no Network Manager icon in the notification area of my top panel, and that the Network Connections setting dialog has everything grayed out. All was working properly on 10.04, and it still works when booted into WinXP.
What diagnostic data is needed to troubleshoot this? Let me know and I'll provide it (if the not-fully-capable system will give it to me)...