Blank white pages is a PHP error that for some reason the error messages don’t show because your server is not setup to display the errors. The 500 Internal Server Error means something has gone wrong but the server cannot specify the state of the exact problem.
Follow the below steps.
1). Set your “Output Compression Level” to 0 in the System > Settings > Server tab.(open cart only)
2). Then open php.ini and add the following code:
display_errors = 1; error_reporting = E_ALL; log_errors = 1;
3). If the file php.ini cannot be read by the server, use an alternative method. Open index.php and add the following code below at the top (line 2):
ini_set('display_errors',1); ini_set('log_errors',1); error_reporting(E_ALL);
4). When you have fixed the problem, remove code line above.