Okay,
The html includes page writes to files in the includes folder.
There is a php file for each of the sections.
Header.php,footer.php,Etc,Etc
I would check that folder.
And see if your server is reporting any server errors.
For me the folder is set to 777 and the files are 666.
It could also be the server has been changed as far as group ownership of the files and you are not the owner of the folder or file anymore.
That would be resolved by contacting your host.