Header no send?!
That doesn't sound like Apache to me.
I'd try restarting the webserver, or restarting the entire server actually, just for good measure. Personally, I have no Idea what the problem is, other than it must be with Apache and not PHP.
if that doesn't work for you, you could try to flush() the header
<?
header("Content-Type: text/html;\n");
flush();
?>
the flush() function attempts to force the current buffer to the browser, but if Apache no write header, you've got biiiiiiiiiiiig problem.