Unable to access the .onion site with Tor.

Hello.
Indeed, it's risky to ask this question here; if any mods see this topic, they might delete it.
Anyway, to answer your question, my dear Kleamolete, you really need to be aware of all the recent .onion URLs to access them. It's quite simple to explain. Even though it's on Tor, and thus the "authorities of the Internet," if we can say so, can't access the users of the browser itself, they can, however, block the URLs and make them inaccessible by making it seem like they don't exist.
For that, you need to search for the most recent .onions using Tor and enter them into the URL bar until it takes you to the actual site. (Well, it depends on the site you're looking for; if it's for The Silk Road, for example, it will be quite easy to find, as it's one of the most well-known .onion sites.) However, be careful: even if you can keep the .onion URL thinking you now have constant access to the site, the URL can change at any time and completely unexpectedly.
There you go, have a great day on the Deep Web :D