MediaHound

Type the page you want to go to in the address bar in the top, then click "Go". Next, click "add this URL", and it will add it to your list on the left. You then type your username and password so the software stores it. FYI, it stores this list in your program files on YOUR computer, so these passwords are never shared with anyone.
The first page that shows up when you start up the software is a list of forums from forumtopsites.com - maybe the server was down for a moment the time you tried to view it. That would "give you the page cannot be found" error. Either that, or if it's not connecting to the internet at all, even when you type the address of a board you know is working, you might need to allow the software access to the web in your antivirus because antivirus is designed to not allow so many programs the ability to access the internet. You need to think of why it can't connect and bypass that or add it to some whitelist.
First, just try again and see - mine works fine, that site is up...