What is the text editor that you use on your site? It is obviously making a mess.
the html code that one has in the editor needs to be saved without <html> and <body> tags -> this is something that your editor doesn't do. My advise would be to change to another another one such as tinymce or JCE and then delete the whole description of your category and write it again.
right now your description contains invalid tags such as <html> & <body> and that breaks your page.
Cheers,
Daniel
