Featured Image not showing at all

Whenever I add a featured image to my page/post it doesn't show at all. The main header from the homepage is displayed instead. I checked the settings and made the main header show only on the homepage and that caused the featured image area to disappear completely from pages... Once I restored it, the main header came back to all pages, but I'd like to display different featured images on my pages/posts. What to do? Is the Featured Image option only available when one has the PRO version of the theme??? So far I have no plugins so the problem doesn't lie in the plugins for sure... Any idea what to do?? I'd be grateful for any hints.