Fatal Error Message when trying to access “Pages”

I’m getting this error message when I click on “Pages” to try to edit my site: Fatal error: Call to undefined function esc_html_x() in /home/cwclaire/public_html/wp-admin/edit-pages.php on line 144

It is a link, and when I click on it, I get this message: Warning: require_once(includes/meta-boxes.php) [function.require-once]: failed to open stream: No such file or directory in /home/cwclaire/public_html/wp-admin/edit-page-form.php on line 76

Please help! I have a deadline on this site…..

It is https://www.iouako.com Maybe the problem is visible to someone who knows more about this.

Thank you so much!!!!!!!