If you cannot ping any websites and cannot get updartes or upgrades, you might have a nameserver issue. GI just installed a fresh copy of Ubuntu Server 12.04 and this has been an issue since I installed it. I did not know what to do, but I check the /etc/resolv.conf file and it was totally blank. The format for this should be (as a sample)
nameserver OTHER ROUTER
You might need to tweak this a bit, I just wrote the same router twice. Save the file, exit and voila! Internet connection again!