If you get the White Screen of Death, it's time to call up your favorite hosting company. WP Engine will be able to troubleshoot and tell you why your Wordpress site has gone down. They can also help you revert back to the last save. Just a reminder, it's always good practice to back up you site before and after your work. If you complete something particularly complex, go ahead a back that baby up. No point in losing all that work. 

Your hosting includes amazing 24/7 WP Engine support service. Do not hesitate to call them at 1-877-973-6446.