Wordpress upgrade/theme issue

Yesterday, I uploaded and activated a new theme on my blog, Http://mommyismoody.com. This afternoon, I backed up my database, then manually upgraded to Wordpress 2.6. Since doing so, I’ve noticed two things:
-when I view my domain, it ‘stretches’ the content area to the width of my screen;
-the Wordpress admin panel does the same thing, giving it an almost ‘css-free’ look.

My sub-domain’s admin panel and theme are not having this issue, so I can’t see it being a purely WP2.6 problem. I’ve tried deactivating my plugins, clearing my cache and reopening the browser. Any theories?

I’ve arrived at the end of my rope with it, since now not all of the visual editor buttons are appearing in the ‘New Post’ page.