Common Errors : Wordpress website turn to blank , website not opening .
Troubleshooting : If you enable debug mode, You will get the error details
PHP Warning: Use of undefined constant REQUEST_URI - assumed 'REQUEST_URI' (this will throw an Error in a future version of PHP) in /home/username/
How to Fix:
Mostly The problem could be related to an outdated or conflicting plugin. Please try to log into wordpress portal and disable all plugins and see if the site loads properly.
If it does then you have to try and enable plugins one by one to determine which is causing the problem.