I had same problem check your log files and you should see a fatal error memory size issue etc.
Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to
allocate 122880 bytes) in
/home/domainfolder/public_html/wp-admin/includes/menu.php on
line 126
you need to enter the following line into wp-config.php
define('WP_MEMORY_LIMIT', '512M');
I also changed memory_limit in php.ini from 64M to 512M
Then it worked fine.
hope it helps.
I am using backWPup now. I will check it though. nice share.