One problem that I frequently hit is the 404 Not Found error. A site is defunct and can't be accessed at all. Most forums seem to have dead links.
There are several solutions, one is Google caching which I know nothing about.
Another is the Wayback Machine, a site that will resurrect a dead link, see:
http://web.archive.org/collections/web.html
Right click a dead link, choose Copy Shorcut and paste into the Wayback Machine's "Enter Web Address:" box. You will first need to delete the pre-existing "http://".
Facebook pages: it seems that it is usually blocked by "Robots.txt"!
It will show all the major revisions to a web site. You may or may not hit an error with attempts to access the very last revision, if so choose the second last revision.
Wayback Machine is not a Google-style search engine, rather it accesses its own database of stored web pages. Database goes back to about 1996.