When I run my index.php with the following doctype:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
It works in both Chrome and Firefox everything is displayed. The problem is in IE9 it just shows the html sourcecode.
Now I know it't not the code because when the file extension was index.html it displayed fine in IE9.

I've also tried

<!DOCTYPE html>
Which is ment to work with all the new browsers. Probably a stupid question but anyone shed some light?