Can no longer access administration pages - Warning/Error
go to your settings.php and add this code below 

error_reporting(-1);  // Have PHP complain about absolutely everything 
$conf['error_level'] = 2;  // Show all messages on your screen, 2 = ERROR_REPORTING_DISPLAY_ALL.
ini_set('display_errors', TRUE);  // These lines just give you content on WSOD pages.
ini_set('display_startup_errors', TRUE);


follow these steps Blank pages or "white screen of death" (WSOD)