@george1421 thanks!
i look into the apache error log file and it help me to figure out what’s the problem.
this is the error
all i had to do is change the /etc/php.ini file
change max_execution_time from 30 to 300
and it’s all work now 
PHP Fatal error: Maximum execution time of 30 seconds exceeded in /var/www/html/fog/lib/pages/snapinmanagementpage.class.php on line 652, referer: http://132.70.33.80/fog/management/index.php?node=snapin&sub=add```