I recently tried to update one of my WordPress plugins that somehow managed to bring my whole site down. I was unable to go to wp-admin to disable the plugin. I had to first disable all the WordPress plugins manually (through phpMyAdmin on my server) so I can get to wp-admin page, and then reinstall the plugin that caused the problem.
The best thing about this approach is that you don’t lose your existing configuration settings for the WordPress plugins (except for the one that caused issues in the first place).
Here are the detailed steps on how I went about getting my site back up.