PROBLEM: Site showing only one certain article!

Hello… I’m using WordPress since years and i’ve never seen such a strange problem on it…

I’m actually renovating my site on a new host service. I was working on it. And i was specially adding / changing / modifying categories. And then i checked the site and discovered that all of the posts are replaced by the last post written of the default category.

When we see the index page, the titles and some other properties of the posts are normal. But when we click on them, even if we see the correct URL on address bar, the content of the post is always the same – that is the last post of the default category as i mentioned.

Here is my site: https://www.s39816.gridserver.com/

Click on one of the articles you see in the middle of the page. Then click on one another. You’ll have always the same content in different URLs.

Is there someone who could have a solution?

Thanx

Erhun