Web pages can be hosted on computers just like the one you're using now, although most of them use hosting services with many computers. Sometimes, they aren't working. They get shut down, or the means by which they are contacted isn't working at the moment. There can be many reasons.
It's not something you can fix; that's up to whoever maintains that website. For what it's worth the page you attempted to load is working now, but my "now" is your "then". So... it's reasonable to say that now and then, web pages just don't work.
Try some other time — in the future, when it will be "now" again.
Here's what that web page looks like now, which is to say, at present, which will no longer be "now" the moment after I post it.

That is an archived version of what that web page looked like on September 30, 2008. That was then.
This is now:

... and now, it is no longer Now. It is Then. Or was.