Please try repeating the steps after enabling error debugging on your PrestaShop store. You will see some error, just post it here so that we can guide you accordingly.
FYI, to enable error debugging you can follow the steps below.
- open file: config/defines.inc.php (using FTP or hosting control panel)
- change false-->true:
define('_PS_MODE_DEV_', false);
define('_PS_MODE_DEV_', true);