Nearly in Tears! Appearance > Menus is Missing Options

Hi,
I am desperate for help! I’ve spent days trying to figure this out and I am nearly in tears.

The Appearance > Menus button is visible on my dashboard, but when I click on it, it takes me to a blank page and the menu options don’t show up. My menus are still on my site, but I can’t alter them in any way. Where did the menu options go?

What I’ve tried: I just upgraded to 3.2 and updated my theme too (Pagelines PlatformPro), but was previously having this issue so I don’t necessarily attribute it to these upgrades. I have deactivated all my plugins and still have the issue. My host has the necessary PHP and MySQL versions. I have switched themes– Twenty Ten, Twenty Eleven– and the problem remains.

Thank you very much for your help!