WP Admin, some sections not working, tried everything…

Problem visable in Admin. When viewing the site externally you can’t see problem (except sidebar configuraton cannot be changed)

In WP Admin, when I click on Customize, Header or Background, I get a white screen except for the top left corner where I see this non-html text:
Edit Add Image
Image
Title:
Choose an Image

When I go to Widgets, the right side of page is white. There is no sidebar setup. The only stuff on the page is the Available Widgets on left side. These Widgets cannot be dragged or moved.

I have:
Disabled all plugins
Switched theme to: 20/14, 20/15, 20/16
Same problem.

I have:
Re-installed WP via admin panel
Manually, via FTP, installed a fresh Admin folder and files and Includes folder and files.
Contacted theme developer, one specific plugin developer (AI1EC, sidebar calendar) and my host (HostMonster) and they all have sent me here.

Is there anyone who can help? I can say “thank you” via PayPal.

http://www.troop172newpaltz.com

Thanks