can't access admin/manager screen

I'm using:
PHP version 5.4.24
MySQL version 5.5.40-36.1-log
not sure how to tell which ModX version we're using.

I type in ourwebsitename.org/manager and I get a blank screen. This was where I could previously log into the modx manager and update our website content.

Can anyone please help?

thanks!!
Ben

The first thing to try is deleting all files in the core/cache/ directory. If that directory doesn't exist, you're using MODX Evolution.