WordPress update leads to 404 error on admin page and signup. CSS mishap with all plugin related functions

First of all never update production/live version, download it and try it locally or on dev server.

http://bubblz.in/wp-admin seems working for me. Check do you have still page named login-page.

For conflict css files you will need to remove them.

add_action( 'wp_enqueue_scripts', 'wp_remove_theme_enqueues', 11 );

function wp_remove_theme_enqueues()
{
    if( is_ThatPage()//search for that page ) 
    {
        wp_dequeue_script('cssFile');
        // etc
    }
}