WordPress Update: Dashboard Gone

Hi, first of all you can try to overwrite the wp-admin folder using an ftp client, if that doesn’t the next step is to deactivate all plugins and switch to the default theme: you can do this using the databse -> phpmyadmin or ftp,I’d recommend ftp just rename the plugins folder to old.plugins (this will deactivate all plugins) and also rename the current theme to “oldthemename” (this will disable the theme and activate twenty eleven.
Hope this clears the error,
Regards