I know it’s happened to me, and it’s probably happened to you. No, I’m not talking about forgetting a website’s address or forgetting where your bookmark/favorite is. I’m talking about the site that had good information — but the site is not there any more.
Sometimes, the site might be an online games site or such as that. If you are looking for interactive content or downloads you would have found there, try Google — www.google.com. Remember the mantra “Google is our friend.”
If you are looking for content, though, you have a real good opportunity to find a copy of the site on the Internet. Not a pirated copy of the web site, but an archive.
Check out the Internet Archive (http://www.archive.org/) to find all kinds of data from the Internet’s paast.
If you know the URL of the website you seek (you did find the bookmark, didn’t you?), you can enter it in the site’s “Wayback Machine” search box.
The Wayback Machine will give you access to occasional snapshots of the site’s content. It does not key to each change of the content at a site; it is just a snapshot at some point in time. For some sites, it’s every month. For others, it is less frequent.
One of my reference sites for Windows XP services is/was called BlackViper.com. It’s not operational now and gives an “under construction” page. The Wayback Machine still lets me access the content when I need or want to read something.
UPDATE: BlackVipre.com is back alive.