Upload the file to the same folder of conf_global.php via FTP:
constants.php
then once you're in, disable apps and plugins. This will give you access to your ACP again.
After disable apps and plugins, delete the file you uploaded (constants.php).
To find out the resource with issue, you will have to enable one, test, enable other, test, etc... or maybe you'll find out which one with problem in the logs.