Probably a bad plug-in that was broken by the newer version.
Add this to your includes/config.php file and see if the white screen goes away.
Code:
define('DISABLE_HOOKS', true);
If it does you know it's a plugin. Then go in and turn off all your products and independent plugins. Comment out the line you added to config.php. Then you can turn on each product and see which ones white screen you. You should be getting the error email for those errors by the way.
Look for updates and issues for each plugin where you got them.
