I had my mce editor disappear as well, happened just the other day. It turns out it was a plugin ([url=http://wordpress.org/support/topic/allo ... ?replies=1
]Allow PHP in Posts and Pages[/url]). I would suggest trying again on disabling all plugins, seeing if it works, then if it does re-enable them one by one until you find the one that is breaking the mce (a lot better than reinstalling wordpress and finding the mce doesn't work because of a plugin.) Next, if you are still having trouble, try re-uploading the wp-admin & wp-includes.
One thing I found when I was dealing with this was neither tiny or ultimate mce would work.
However the Ckeditor did work. http://wordpress.org/extend/plugins/cke ... wordpress/
Hope this helps!