Embedded hyperlinks and HTML editor both broken

Hi all,

Basically, without really knowing how or why it has happened, my blog has stopped allowing me to imbed links into the posts/pages and at the same time I lost the ability to be able to edit my posts/pages in the HTML editor.

Embedding links
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When I am in FireFox, the embed link pop-up box appears and I can enter the link into it, but when I click on it, it doesn’t do anything.
When I am in IE, the embed link pop-up box produces an IE Script Error stating: that there is an object expected and on the url: http://blog.christopher-morgan.co.uk/wp-includes/js/tinymce/themes/advanced/link.htm

HTML Editor
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In both browsers, trying to open the HTML editor gets a pop-up box with the following: {$lang_theme_code_title} and an empty text box with an update or cancel button.

I’ve tried replacing the contents of the wp-includes folder but it has made no difference. Can anyone help?

Thanks in advance.