I have set up a new Moodle 2.8.5 site for a client. Today while testing I ran into the “white screen of death”.
Up to now the site has been running fine. Also, my localhost copy, which is an exact copy, is also running fine.
While fiddling about I got the message that I needed to enable the JSON extension for PHP.
Because I could not get around the problem, and since it’s a new site, I decided to do a quick reinstall. I commented out the config.php file and started the reinstall, only to run into the JSON extension issue.
Checking my server PHP settings made me realize that my service provider had sneaked in a PHP 5.6 upgrade. Fortunately they had left in the switch to set the PHP version back to 5.4
Once I had done that, the site was back up and running with no problems.
This may not fix everyone’s problem, but if certainly fixed mine.