Here is the solution.
I have de-enabled all the plugins but one.
I have activated the default WP theme.
Thanks to one plugin (WP-DB-Manager), I emptied the wp-options line in the database table. Then, I went in the settings, and set my preferences.
Under the appearance/widgets, the TEXT and CATEGORIES widgets are here. :-D
Now, I will re-install one by one all my plugins, and put up my WP FrameWork theme. I will see if all goes OK.
Will keep you updated,
P.S.: I think that WordPress code should have a way so that such a problem does not pop up.