I'm not sure what happened to your installations, but checking the source code in your website @lavishbride, the code that's showing up is code that is in v1.5.1 where the search form is right below the site title.
<div id="inner-header" class="clearfix">
<h1 id="site-title"><a href="<?php echo home_url( '/' ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a></h1>
<h2 id="site-description"><?php bloginfo( 'description' ); ?></h2>
<?php get_search_form(); ?>
while on v1.5.2, the call to
<?php get_search_form(); ?> is done after the main navigation and uses css to position it to the top right corner.
This is why I thought you were using a child theme and copied the old
header.php file from v1.5.1.
Anyway, can you try switching to a different theme then switch back? see if that clears things? If you have a caching plugin installed, could you clear the cache too?