When you're having network issues and can't access the Internet, isolating the problem isn't always easy. As Ghacks points out, many computer systems have networking tools available to help you figure out the issue. Tools like ping, traceroute, nslookup, and netstat, are all proven utilities that help identify network problems.
If you're not familiar with using those tools or would like a simpler all-purpose tool, Google has created a Chrome app called Chrome Connectivity Diagnostics. It contains several different networking tests with the results displayed in an easy-to-read format.
After installing Chrome Connectivity Diagnostics from the Chrome Web Store, start the app from the Chrome App Launcher to begin running the tests.
To display all the tests and the results, click on the gear icon and select "Show passing tests." Clicking on the individual tests will provide a brief description of the test and a link to the logs.
That's it. If you happen to be on a Chrome OS device, you'll also notice two additional tests: Wi-Fi signal strength and default gateway is reachable.