One reason why you might not get an error is because of: @
Get rid of them. All of them. You should code in a way that your queries do not throw unwanted errors, not try to hide the symptoms.
The reason for not executing are two-fold:
- The folder might be outside your webroot
No real solution, but to change your server configuration, I think
- The include file is in a subfolder
include('folder/db.php');