As I mentioned above, double-check the templates at the top of the Templates tab in Manage Articles. The one on the left should be the container template, not the article template.
Try creating an Article by right-clicking on the Articles container and selecting "Manage Articles," then click on the "New Article" button. See if the new article shows up. You'll also see if the existing articles show in "Manage Articles."
You might look in the DB in PhpMyAdmin. Check the modx_site_content table. If you sort by class_key, the articles will come to the top. See if the parent field of the articles matches the ID of the Articles container document you're using.
As a last resort, I would uninstall and remove Articles and delete all the containers you've created. Then re-download and re-install it and create the container in the MODX root. You'd lose any articles you've created, but it would be a fresh start.
The Articles uninstall used to be pretty ugly and incomplete, but I think that's been corrected in later versions.
If all that fails, some people use the Collections extra for blogging, though I think it's more complicated to set up. A recent addition is
BlogIt, which uses Collections to create a blog. I've never used it.