Hi @yasser,
Once your server has been accessed by a hacker, it’s good policy not to trust anything on it. As usual, your PHP error log will probably indicate an error message that corresponds to the blank page, but I would suggest either replacing your OJS code with a fresh copy (and reviewing everything that you haven’t replaced), or using a standard tool like diff to compare your installation against the stock version of the same release.
Regards,
Alec Smecher
Public Knowledge Project Team