Plugin settings values not save wordpress

I am working on a plugin settings. First I save plugin settings in normal way and it works perfectly

Here is my old code:

index.php

add_action('admin_init', '_register_settings');
function _register_settings() {
    register_setting('_settings_group', '_plugin_slug');
    register_setting('_settings_group', '_article_qty');
    register_setting('_settings_group', '_search_setting');
    register_setting('_settings_group', '_breadcrumbs_setting');
    register_setting('_settings_group', '_sidebar_home');
    register_setting('_settings_group', '_sidebar_inner');
    register_setting('_settings_group', '_comments_setting');
    register_setting('_settings_group', '_bgcolor');
}

and in settings.php

<?php
    if(isset($_GET['settings-updated'])){
        echo 'Settings updated successfully';
    }
?>
<form method="post" action="options.php">
<?php  
     settings_fields('_settings_group');
?>
<input type="text" name="_plugin_slug" id="_plugin_slug" value="<?php echo get_option('_plugin_slug'); ?>">

// Same other input fields

<input type="submit" value="<?php _e('Save Changes','foo'); ?>" name="submit" id="submit">

It save my values perfectly but now i change the code to register settings and call its values but its not working, whenever i save values it shows me a blank page after i submit the form.

Here is my new code:

index.php

add_action('admin_init', '_register_settings');
function _register_settings() {
    register_setting( '_settings', '_settings', '_validate_settings' );
}

function kbe_validate_settings( $input ) {
    $_clean = array();

    $_clean['_plugin_slug'] = isset( $input['_plugin_slug'] ) ? sanitize_title( $input['_plugin_slug'] ) : '';
    $_clean['_article_qty'] = intval( $input['_article_qty'] );

    $_clean['_search_setting'] =  isset( $input['_search_setting'] ) && $input['_search_setting'] ? 1 : 0 ;
    $_clean['kbe_breadcrumbs_setting'] =  isset( $input['_breadcrumbs_setting'] ) && $input['_breadcrumbs_setting'] ? 1 : 0 ;

    $sidebar_positions = array( 0, 1, 2 );

    $_clean['_sidebar_home'] = isset( $input['_sidebar_home'] ) && in_array( $input['_sidebar_home'], $sidebar_positions ) ? intval( $input['_sidebar_home'] ) : 0;
    $_clean['_sidebar_inner'] = isset( $input['_sidebar_inner'] ) && in_array( $input['_sidebar_inner'], $sidebar_positions ) ? intval( $input['_sidebar_inner'] ) : 0;

    $_clean['_comments_setting'] =  isset( $input['_comments_setting'] ) && $input['_comments_setting'] ? 1 : 0 ;

    $_clean['_bgcolor'] = isset( $input['_bgcolor'] ) ? sanitize_hex_color( $input['_bgcolor'] ) : '';

    return $_clean;
}

and in settings.php

<?php
    $_defaults = array( 
        '_plugin_slug' => 'Knowledgebase',
        '_article_qty' => 5,
        '_search_setting' =>  0,
        '_breadcrumbs_setting' =>  0,
        '_sidebar_home' => 0,
        '_sidebar_inner' => 0,
        '_comments_setting' => 0,
        '_bgcolor' => ''
    );

    $_settings = wp_parse_args( get_option( '_settings' ), $_defaults );
?>

<form method="post" action="options.php">
<?php  
    settings_fields('_settings');
?>
<input type="text" name="_settings[_plugin_slug]" id="_plugin_slug" value="<?php echo esc_attr( $_settings['_plugin_slug'] ); ?>">

// Same other fields

So where am I making a mistake?