I've spent more than half an hour trying to open my company's SharePoint 2013 site in SharePoint Designer 2013. There were no errors - just several identical dialogs showing the prompt for credentials (there were 3 or more of them), and then... nothing happened. I wasn't able to find the log file for SPD, so I went googling for the solution.
It took me several hours to dig through the Internet checking all sane pieces of advice.
