Thank you Ethan,
i have a backup of the htaccess file, i simply replace it and all goes right again, you can take the defaut joomla one.
its had the same issue as mentionned on the end of the article as Yootheme and Zoo, some images and css are not loaded, they suggest to add some exception to the file like :
RewriteRule ^templates\/your_template_folder/ - [L]
## I found this necessary for @fontface fonts
RewriteRule ^templates\/your_template_folder\/fonts/ - [L]
##Yoo Themes Widgetkit and Zoo will not display css styles or images correctly if the cache folder access is blocked
RewriteRule ^cache\/widgetkit/ - [L]
RewriteRule ^cache\/com_zoo/ - [L]
RewriteRule ^cache\/com_templates/ - [L]
RewriteRule ^cache\/template/ - [L]
RewriteRule ^cache\/plg_jch_optimize/ - [L]
i was wondering how we can add Easydiscuss and other extensions here !
ps: this tip is provided by the official joomla team