Dashboard Whitescreen of Death?

You have active a plugin or theme, that include scripts or styles via function wp_enqueue_style and wp_enqueue_script. Since version 3.3 is it not possible to enqueue script and styles without a hook. Find the source and fix this, is easy to do that. The codex have for this topic a fine documentation.

/**
 * Proper way to enqueue scripts and styles
 */
function theme_name_scripts() {
    wp_enqueue_style( 'style-name', get_stylesheet_uri() );
    wp_enqueue_script( 'script-name', get_template_directory_uri() . '/js/example.js', array(), '1.0.0', true );
}

add_action( 'wp_enqueue_scripts', 'theme_name_scripts' );

The same problem is on the your widget topic.
To find the right plugin or theme, deactivate all plugins and switch to default theme. Switch on step by step and check.