Blank screen with a dot on ALL of my installs

Hi

I have about 8 or 9 clients websites on my servers, all running different themes, some custom, some not, different plugins etc.

I had a client say they cant login and I checked and after entering the password, I get a bank screen with a dot on the wp-login.php page.

This is very odd that its happened on every domain.

I have tried almost everything I can find, like renaming template/plugin folder, checking the content of config.php and settings.php etc etc.

Is this something to do with the auto updates that happen now? Can you shed any light on why this is happening?

Thanks