Check that opcache, mysql, mysqli is checked, if not the case check it, and 'save'
If you have a blank page, it means that one of your modules is not compatible, search your error_log....
Also, you must read about :
https://support.yoorshop.hosting/knowledgebase/1119/Send-emails-with-prestashop-wordpress-and-other-CMS-with-phpmail-by-default.html
Thursday, September 3, 2015