There are plenty of examples out there of WordPress installs suddenly displaying blank pages—on admin pages as well as frontend posts—after changing themes, adding/removing plugins or updating the WordPress backend. Whilst there is plenty of good information out there covering most of the usual suspects, I just came across another which was fairly difficult to track down given the lack of information, though pretty easy to solve once I’d found it. If like me you’ve at any point tried to streamline your WordPress install by cutting down on a few unnecessary services, and reducing the number of calls to the database, you may have added some lines to your wp-config.php file like so:
define('TEMPLATEPATH', '/path/to/theme/directory');
define('STYLESHEETPATH', '/path/to/theme/style.css');
Fairly innocuous, until you actually change your WordPress theme, in which case those long forgotten about resource savers will leave you with little more than a blank page to diagnose your problem. If this is the case though, just updating the lines or commenting them out will leave you with a workable system once again.