Hide comments and posts posted by other user

You can use a filter to pre_get_posts so that only your posts are listed. Something like this:

function my_posts_only( $query ) {
    global $pagenow;
    if ( 'edit.php' != $pagenow || ! $query->is_admin )
        return $query;
    if ( ! current_user_can( 'manage_options' ) ) {
        global $user_ID;
        $query->set( 'author', $user_ID );
    }
    return $query;
}

add_filter( 'pre_get_posts', 'my_posts_only' );