Enqueueing Scripts and Styles

I think you are using the wp_enqueue_style the wrong way as it is not an action hook. wp_enqueue_scripts action hook is being used for enqueuing both scripts and styles.
try this:

function my_scripts_method() {

        wp_deregister_script( 'jquery' );
        wp_deregister_script( 'style' );

        wp_register_script( 'jquery', '//ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js' );
        wp_register_style('style', '//siteripe.com/style.css' );
        wp_enqueue_style('style'); 
} 
add_action('wp_enqueue_scripts', 'my_scripts_method');