A blank page normally indicates a PHP error has occurred. However most host providers will disable error reporting to the page to help improve security (error messages can often provide information that will aid in malicious attacks)
The way to find out what the error is, is to enable error reporting within Joomla! which you can do in Site->Global Configuration->server->error reporting
Set it to either simple or maximum.
Load you page up again, and see if an error is shown.
If you still get a blank page, then we to get a little more aggressive,
Edit your /index.php (in the root of your Joomla! install)
and add the following somewhere near the top, within the <?php tag
error_reporting(E_ALL | E_STRICT);
The sadly, the above wil not report parse errors. So if you are still getting a blank page, you need to find out if you have access to error_log which many hosts give these days. If you are unsure, ask your hosting provider for access to your apache error_log file.
Alternatively you can edit your /.htaccess file (create it if it doesnt exist)
php_value display_errors 1
php_value display_startup_errors 1
Provided your host supports user htaccess files, this will show any error your site is generating.
Once you have your error, you can start to figure out why its happening.
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