Fatal Error on Line 20 – Nothing will load

Maybe a plugin is not working correctly with the new 3.5.
Try going into your site via ftp or web host control panel and temporarily remove your plugins. That might give you control back.

@seattlechangingroom: That’s a very common theme/plugin issue. See http://make.wordpress.org/core/2012/12/12/php-warning-missing-argument-2-for-wpdb-prepare/

Force deactivate all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugins. See resetting the plugins folder by FTP or PhpMyAdmin.

If that doesn’t help, rename the active theme folder to force the default theme to load.

@yiannis Girod: start your own post for your own issue.