Big problem with navbar

Hi,

First, sorry for my bad english but i’m not an english man.

So, when i logged on my website, i saw that the navbar was really uggly.
For each parts of the menu, there is a newline. In fact, the menu isn’t horizontal but vertical now ..

Screenshot here : http://uppix.net/99lYhf.png

How to repair that ? 😮

thanks in advance!