Hello,
I am far from a SharePoint expert, I'm just the lucky guy who was stuck managing our SharePoint setup so please bear with me. :) We have a very small SharePoint 2013 farm which has around 6 different sites and uses a SQL Server 2008 R2 back end. The farm/sites have been up and running with no issue for the better part of 2 years now and then suddenly this morning, all of the sites and Central Admin are now only displaying blank pages for all users. I've spent the better part of the day digging into the issue and it seems the vast majority of people with similar issues agree that it is usually an issue with the IIS authentication methods that are enabled for each site. I've tried adjusting the authentication methods to only have Windows, Basic and Digest enabled to no avail. I've also performed the process to disable loopback check, ensured the accounts used for each site and SP service don't have expired passwords, added the central admin site account to the server admin group, all do no avail. At this point, I'm at a dead end with no solid path forward so any suggestions outside of the things I've tried would be greatly appreciated.
Thanks!