PHP redirect is just a blank page

[boost_dependent]

I'm new here, but I figured you guys would know why this isn't working.

I have a site http://mysite.com but when someone types this in I want it to go to http://mysite.com/folder/

I have tried and tried to get the php header redirect to work, but all I get is a blank page.

Here is what I have:
an index.html file with this in it
<?php
header("Location: http://mysite.com/folder/");
?>

There is nothing else in there at all, not even a space. Any help on this would be awesome.

Thanks

[boost_dependent]

Nevermind, I was using an html file. I just changed it from index.html to index.php and now it's working fine.