It seems to me that I can not access into appearance => customise screen. It is blank. Any help? suggestion? Thanks in advance. the site adres is: http://artmediabroker.pl
You can try to deactivate all your plugins except Sydney Toolbox and Page Builder by SiteOrigin, and see if it helps.
Please remember about importance of regular full site backups (files and database):
Also you might want to check this tutorial:
Kind Regards, Roman.