[larry_chmbrs]

I want to block my system from getting to mypage.

[jstrike]

I'm going to assume that you're running Windows... There's two ways you can do this.
1. You can add an entry to your hosts file. Your hosts file is in c:\windows\system32\drivers\etc. Open it with Notepad or any other text editor and add the following lines to the bottom of the file:

127.0.0.1 mypage.com
127.0.0.1 www.mypage.com

Save and close the file.
Close down all your browser windows
Open up a DOS window.
Type: ipconfig /flushdns.
(No need to reboot)
This is quick and easy but there are two problems with it, the first being that if the person you're trying to block has admin privileges to the computer, with a little digging they can easily reverse what you did. The second is that this will only block what you put in here, so mail.mypage.com or any other subdomains that you don't know about, won't be blocked.

The second way is to purchase some software such as Net Nanny or Cyber Patrol. The upside is that it's much more comprehensive in what it blocks, which may or may not be what you're looking for. It's also a lot tougher to circumvent. The downside is not only the cost, but it can take longer to setup.