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When you type a URL into a web browser, your computer doesn't know what it means. So it contacts a computer called a DNS(domain name system) server(it's like an Internet phone book for computers) and finds out the IP address(like a computer's Internet phone number) that it corresponds to. For instance, 72.14.207.99 corresponds to google.com. However, before asking a DNS server, your computer looks at its own list(which stays blank unless you change it). If you change that list to say that google.com is 0.0.0.0(there's nothing there), it'll try to go to 0.0.0.0, but since there's nothing there, it won't be able to load. In essence, you've blocked google! This will work for any other site, too.
If you didn't understand that, don't worry; it's actually pretty simple!
Step 1Open the file
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Open the Start Menu and go to Programs>Accessories>Notepad. Click the file menu, and click "Open". Find the box that says, "Text Documents (*.txt)". Click it and change it to say, "All Files". Copy this(without the quotes) into the textbox above it if you have XP or Vista:
"C:\WINDOWS\system32\drivers\etc\hosts"
or this on 2000:
"C:\WINNT\system32\drivers\etc\hosts"
It should look like the image below(all the other images are the other steps in order).
Really, I got this technique directly from a PC magazine article a few years back. Infact, that's where I learned about the hosts file. This isn't anything original oon my part.
Incidentally, I think (although I'm not 100% sure) that 0.0.0.0 redirects back to you, much like 127.0.0.1. So if you're using your computer as an http server, this method may display the homepage of your site.
You are being cruel and unusual to whoever you blocked it from! That's unconstitutional, you know! At least in the US it is, and I assume it is elsewhere too, but... Whatever.
Although, I guess I can forgive you if you did it to yourself to stop wasting time.