I have the same problem.
I think it started after the latest wordpress update.
This page gave me a solution to my problem: http://codex.wordpress.org/Template_Hierarchy
I had a front-page.php file in my theme and it was that file, not index.php, that got triggered when I set my “full screen image”-page as the front page. When I removed it wordpress worked it’s way through the hierarcy and found my custom template.
This might not be the best way to solve this, so if you have a better soultion please let me know.
Does you them have a content.php file?
The get_template_part functions tries to find the content.php and use this to format the post. This file might contain HTML that results in the missing sidebar and footer.
You should check the HTML source for your page to decide if it the sidebar/footer are missing, or just not visible. Ctrl-U in most browsers.
