Admin CP left frame disappears

[TwinsForMe]

I log into the Admincp and I see the left frame and the large right frame. If I click on something in the left frame, I jump to what I clicked but the left frame disappears. Can someone point me in the right direction, please?

[Marco van Herwaarden]

What hacks you recently installed? Any of them made changes to admincp/index.php?

You have some screenshots?

[TwinsForMe]

This started right after I installed Photopost Classifieds. But it seemed to have solved itself. Weird.