Pages displaying blank ONLY when Theme Developer module turned on
This might be due to version compatibility with Simplehtmldom module. 

Download this library and install in your sites/libraries files. 

This is taken from modules page,


  NOTE: Currently, Theme Developer does not work with the latest version of simplehtmldom API. You must use simplehtml API version
  7.x-1.12 if you want Theme Developer to function properly.


OR if that is not the case you can try putting this snippet end of  the settings.php file, this snippet will show error message on the browser while loading page instead of WSOD. and you can put your error message here in question and elaborate it.

  error_reporting(E_ALL);
  ini_set('display_errors', TRUE);
  ini_set('display_startup_errors', TRUE);