Columns appearing at bottom of page, blog broken after trying many fixes

I was experimenting with some Twitter plugins for my WP tonight. None of them were working. As I tried each one, when it didn’t work I deactivated and deleted it. I got sick of trying, removed the last plugin, and suddenly my blog is utterly broken. See my blog

I looked at all the theme’s files to see if I could spot some change, but I couldn’t. I tried switching to another 2-column theme. It was still showing the sidebars at the bottom. I switched to a 1-column layout. That made the first column appear properly. I then switched back to my main theme, and it was broken. I can’t for the life of me figure out what is wrong.

I looked on my server, and there are no remaining files from any of the plugins I tried. I did get a strange PHP 5 required error with one of the plugins (I have PHP 4), and another caused a fatal error and could not be activated. I have no idea what file(s) may have been corrupted or how to fix it.

I really need some help fixing this please. I cannot leave my blog in this state.