Withoutseeing you cart site I have to assume that you have not broken the default code.
Look at a copy for your templsate of /common/tpl_header.php and the highlighted code is the constant used that you will replace with your anchor href text
Code:
<div id="logoWrapper">
<div id="logo"><?php echo '<a href="' . HTTP_SERVER . DIR_WS_CATALOG . '">' . zen_image($template->get_template_dir(HEADER_LOGO_IMAGE, DIR_WS_TEMPLATE, $current_page_base,'images'). '/' . HEADER_LOGO_IMAGE, HEADER_ALT_TEXT) . '</a>'; ?></div>