The most common cause of this problem is that the homepage has not been set.
To do that you need to create a page with a homepage/frontpage template applied to it (most likely you have already done this step) and then go to Settings > Reading and set this page to be your Front page as displayed in the image below. Save and check your homepage again.
Since this is a more generic issue it might not apply in all our themes. Please open an new thread in our support forums in you need additional assistance.