post_templates.php file not responding

[Coasting]

My site stopped displaying thumbnails for new posts and at the same time stopped showing the custom field for thumbnails and text at the end of the post editor somewhere along the line this last year.

Am trying to figure it out finally.

Web Address: http://www.coastinghome.com

Found links that talk about "showing" the custom fields by editing the post_templates.php file...only after modifying it to be editable in my FTP program, wordpress isn't recognizing that it's actually editable and still displays the message that I need to see the Codex before I can modify the file.

Any help would be much appreciated!