If you have been using WordPress for a few years you have encountered this at least once. It is frustrating but does not mean all is lost.
Sometimes it only affects the admin panel, sometimes only parts of it.
Here are a few solutions should you encounter the dreaded white screen:
First make sure you have sufficient backups
Check you have not exhausted your memory limit. This could be caused by various issues like bad coding, incorrectly functioning plugins or issues with your web hosting server. Since you have yet to find the culprit you may have to spend some time doing a bit of troubleshooting.
Try disabling plugins, one at a time ,to see if maybe the problem lies with an incompatible plugin that was uploaded. This has happened pretty often and is usually the issue.
Go back to a default theme. It may be the theme that has caused the issue, you will then need to check your functions.php file for issues.
If none of the above fixes it, then you should try to re-install a fresh copy of WordPress. While it is unlikely, but it is always possible that a core file may have been corrupted.
Sometimes, you may have access to the back end, but the front-end of the site has white screen of death. This can happen because of a caching plugin. Simply empty your cache.
If none of these tips help then it’s time to give us a call so we can investigate and get your site up and functioning again.