Sounds like a namespace conflict. You know (cannot redeclare function foo(bar), already declared in...). You should put some error checking code in your index.php file to tell you exactly where the blank screen is coming from. (I'm assuming by "blank screen" you mean the "White Screen of Death.")
This code (at the top of index.php) will do the trick.
<?php
error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);
?>