PHP include overlapping problem

[wyu]

Hi, I'm new to php includes, might be a simple problem, need some help.

I'm including a header menu bar into all my existing html files.
I've renamed all the html files to .php
(could that be the cause of the problem?

Anyway, after I included the header, the header is covering(overlapping) the top of the body of the main document.

The picture below is before and after:
I managed to make a work around by including 6x <p>&nbsp;</p> after the include, but surely there has to be a better solution?
Thanks in advance.~

BEFORE:
http://i164.photobucket.com/albums/u24/eiritsu/bfinclude.jpg

AFTER:
http://i164.photobucket.com/albums/u24/eiritsu/afinclude.jpg

[UnlimitedMB]

looks like the php header is working fine.
but your html code must be wrong.