Fatal Error – site disappeared

Have you tried the steps at http://ww.wp.xz.cn/support/topic/update-to-35-is-showing-fatal-error-cannot-redeclare-get_current_blog_id … does sound like some file didn’t get updated properly so downloading the latest version and “re-uploading all files & folders – except the wp-content folder” may be your best bet.

Basically it means the code is trying to load a function called “get_current_blog_id” twice and that can’t happen because each function has to have a specific name. So likely that it is two files because the upgrade got stuck or something similar.