Answer:
If You Can't Access the Web
We'll assume that your Internet was working at an earlier point. If you are setting it up for the first time, the steps listed below were not designed with that purpose in mind. You need to follow the instructions that came with your router or modem.
I've included a series of definitions for the terminology used on this page.
Reboot the Computer
The first step should be rebooting your computer or device to see if that fixes the problem. You'd be surprised how often that simple step resolves issues.
If restarting your computer or device doesn't work, you'll have to check out each potential problem area to see if it restores access.
Check These Areas
The most likely problem areas related to a loss of Internet assess are one or more of the following:
your computer is disconnected from the network (check the network settings;
a proxy has been added to your browser or operating system;
your high-speed modem and/or router needs resetting or is disconnected;
a disconnected network cable (if your computer is wired);
your computer needs to reboot;
your firewall or security software is misconfigured; or
Your software is misconfigured for access to the Internet.
Progress through the suggestions on this page to test alternative solutions. I've presented them in the order I'd likely progress if I were to be assessing the problem and looking for solutions.
ISP Issues
If the issue is with your ISP or (rarely) a regional access issue, the resolution is beyond your control. You'll just have to wait for your ISP or the Internet structure to repair the problem.