Nothing works except front page

Am running Version 2.11.9.6 on ATT/Yahoo — can’t upgrade to newer version of WordPress until ATT/Yahoo upgrades past PHP 4.1.

Here’s what’s happening:

When you click on the main site’s URL, it looks fine, except for a line of strange characters at the top (I’m using the standard WordPress theme, which I loaded up to make sure my specific theme was not causing the problems):

https://stkarnick.com/

But when you click on any link to an article, category, or any other element of the site, all you get is the line of strange characters, nothing else:

https://stkarnick.com/culture/2011/08/11/london-burning-the-apotheosis-of-statism/

That happens in both Firefox and Chrome.

Dashboard opens fine in Chrome, but in Firefox I get the same line of strange characters as on the other pages.

I have an .xml document of the site’s content, and it looks OK. As noted, the articles come up fine on the home page but nowhere else.

Need help! Thanks.