I had the same problem with the missing editor, but I found out that it was caused by an incompatibility with an other plugin. In my case I was using WP Calendar. The editor were missing at the create new post-page and the calendar event pages. I tried to solve the latter by using an older version of WP Calender, but then I came to break the create new post-editor instead.
I managed to solve the problem with WP Calender by making the following changes:
wp-calendar/FormEvent.php: (added "titlediv")
> <div id="titlediv">
<p>
<?php _e('Subject', fsCalendar::$plugin_textdom); ?>
<input id="title"
type="text"
value="<?php echo esc_attr($evt->subject); ?>"
tabindex="1"
name="event_subject"
maxlength="255"
style="font-size: 1.7em; width: 100%;"
<?php echo ($action=='view' || $evt->updatedbypost == true ? 'readonly="readonly"' : ''); ?>/>
</p>
> </div>
and inactivated qtranslate at the calendar administration pages by adding the follwing to my theme's functions.php:
if (is_admin()) {
if(($_GET['page']=='wp-cal-add') || ($_GET['page'] == 'wp-calendar/fsCalendar.php')) {
remove_filter('the_editor', 'qtrans_modifyRichEditor');
}
}
Later I was building an own plugin, which had nothing to do with the editor, and the editor disappeared again.
Apparently qtranslate uses the jQuery function jQuery(document).ready() to do its magic with the editor and if any other script run by jQuery(document).ready() causes a javascript error any following scripts will not run. A look at the browser's javascript console may help to find the offending script.