Responsive Child theme header.php causes problem

I am using responsive theme by cyberchimp and I usually create a child theme to do my editing in the files. I usually can copy as many files in the parent theme into the child theme such as page.php, single.php, header.php,… to edit them.

However, lately I also copied the header.php to edit it. But as soon as I have copied this file and upload it even without editing it yet, I lose the responsive header menu. Removing this file fixes the problem, but then I can’t edit it.

Can anyone know why this happens please?
Thanks