You have not really provided us enough information about your setup to be able to assist you (webserver and ver? php ver? etc.)
You should consult your php error log and post the errors that you are receiving. If you cannot enable php error logging you can turn on error logging in osTicket by editing the main.inc.php.
on line 43 through 45 locate:
#Don't display errors
ini_set('display_errors', 0);
ini_set('display_startup_errors', 0);
and change it to:
#Don't display errors
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
And post the errors reported here.