Only one post shows up

Hi!
I used to have a working WordPress 1.2 installation, and it was working earlier this morning, but I made a post, and now the front page (containing this post) isn’t working. I only get the title and background, and then the post. Nothing else on the main page (including the menu along the side) shows up. The HTML source looks like it’s just been cut off prematurely, as there are no end DIV, BODY or HTML tags.
This is the site:
http://www.higgs-family.net/~jeremy/
I can get a page to appear properly, but it has to be one without the post I made this morning, such as:
http://www.higgs-family.net/~jeremy/index.php?m=200405
I had a look through the post to see if there was anything that might cause problems, but I can’t find it!
Can anyone help?
Thanks.