Category links don’t work

Now it makes me nervous that in all steps the obstacles find me.

First I was this problem: http://wordpress.org/support/topic.php?id=26716
I found a solution for this one here:
http://wordpress.org/support/topic.php?id=26632#post-149803

And it worked well.

However, this time all of my category links became irrelevant. I mean, no matter which category link I click, it automatically orients me through the default category URL. Below is the link of my site. On the top of the green left sidebar you will find my category links. Click two or three of them, and you will see that it will always give you the same (default) category.

Is there someone who has an idea how to normalize it?