[WP] Shortcodes issue

In header.php, I am using do_shortcode(some content) to display it. But it won’t work. No matter what I pass on, either html or html with shortcodes inside, nothing gets displayed. I’ve done checking if function exist and it does, but I can’t figure out why it doesn’t display anything.

Anyone had a similar problem?

EDIT : forgot echoing the content…duh!