hacked?

I left my page alone for a few weeks and when I got back into it, strange things had happened.

On the blog page (but not most of the other pages) the right column has been filled in with the background color. Widgets specificed for the right column are appearing in the left column.

Most of my posts were either erased or disappeared and replaced with this:
" <!--[endif]-->

The footer disappeared on the blog page, but not many of the other pages.

I also had to label as "spam" a series of comments.

The only thing new I had brought into my admin page was a plugin to create a form.

Has this happened to anyone else? Can you tell me how to fix it? I've been able to replace the text on the blog posts, but I have no idea how to get the right sidebar back. The settings on the admin page are correct as far as I can tell and do appear properly on some pages.

I'm very stuck. Thanks for any insight!

Rachael