In case anyone experiences a similar unhappy morning coffee surprise:
I just upgraded my WordPress to version 3.0. I used Automatic Upgrade, and, as one should, I deactivated all plugins before enacting the upgrade. The upgrade was successful, and then I started reactivating the plugins. After activating WP Super Cache, I found myself with a blank Dashboard/Admin screen, something I haven’t experienced before. But at least I was confident about the culprit.
The solution: go into your FTP program and open up the wp-config.php file in the first WordPress folder with a text editor. Then “comment out” the line that defines WP Super Cache.
If you don’t know what that means, about 10 lines into the file’s code, you should find something that looks like this:
define(‘WP_CACHE’, true); //added by yourname on somedate
change it to this (add two hashmarks to the beginning of the line):
//define(‘WP_CACHE’, true); //added by yourname on somedate
and then save the file. That should restore your dashboard.