Welcome to yet another annoying-problem-trivial-solution post!
If your iWeb suddenly decides to not show your websites, or doesn't open, it might be because of a corrupted domain file. Before trying to look for backups, or downloading your already published website, try this:
> Delete /<home>/Library/Preferences/com.apple.iWeb.plist
> Move /<home>/Library/Application Support/iWeb/Domain (Domain.sites2) folder to somewhere else
> Open iWeb (realize that it opens as expected, but without the already created sites)
> Save an empty website
> Close iWeb
> Move the old Domain file back to its location (overwrite the existing Domain)
> Open iWeb (hopefully you'll see the sites as before)
I hope this solves the problem!
