Add jQuery to WordPress page

I think wordpress only loads jQuery when you specify it is a dependency for another script that is loading on that page:

wp_enqueue_script( 'script-name', '/path/script.js', array('jQuery');

If there is no other script then try loading it like a normal script with full path to the file:

wp_enqueue_script( 'myJquery', '//ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js');