First, do a "view source" of the blank page just to see if anything "interesting" did get output, but in such a way that the browser would not display it.
If not, then you probably have a syntax somewhere, along with the PHP configuration [FONT=Courier New]display_errors[/FONT] set to false. If you use a decent editor with PHP syntax checking built into it (I use Komodo Edit, but there are many others), it should show you most syntax errors so that you can fix them before you even start testing.
Next choice is to look in your PHP error log, and the last step (if we're talking about the live site) is to change your PHP configuration to turn [FONT=Courier New]display_errors[/FONT] on (generally not a good thing to do on a live site). To find out what php.ini file you are using and where the error_log is, just create a PHP file with the following:
<?php
phpinfo();
Open that page from your browser, and look under the "Loaded Configuration File" setting and the "error_log" setting (local value) to see what files are being used.
