There is supposed to be a lengthy post on the first page regarding an intro to the site and it wont show up or replace the old one.
When you keep creating sticky posts they do not automatically "replace" the ones that went before. You must edit the posts the went beforeand remove the sticky designation.
Also if you wish to have a static front page then there is another approach that you can use. Do note that returning visitors aren't keen on having to click through a page with the same blah, blah, blah when they arrive to read your fresh content. Sticky posts and static front page tend to be traffic killers.
Create two static pages. One will be your blah, blah, blah landing page which will become your front page. The other will be a page for your posts to appear on. After you have created them you can reassign them on this page > Settings > Reading
Front page displays
__Your latest posts
A static page (select below)
Posts page: __
Lastly, note the reason your front page is displaying a 404 (page not found) is because you deleted the Hello World post. That will disappear as soon as you publish a post, not a page.