I am posting this question and answer from link because I faced the same problem, and the solution in that post was helpful to me.
Question from the link:
I have an Acer C720 Chromebook, running a dual boot of Chrome OS and Ubuntu 14.04.
When using Chrome OS, I can connect to and use private and public wireless networks with no problems. With Ubuntu, I can also connect to all networks, but with the vast majority of networks I have tried, I cannot use the Internet; the standard 'Server Not Found' screen appears when trying to load up web pages, for example.