The situation is familiar. You pressed activate, the screen went blank, and now you cannot get back into the admin to remove it. The way out is that a plugin can be switched off from outside WordPress too, because WordPress works out the state from the directory structure.
You need FTP or SFTP access or the file manager in your hosting panel. Making the connection is covered in our guide to FTP and SFTP. Go to the directory wp-content/plugins. You will see one folder for each installed plugin.
If you know which plugin brought the site down, add something like -off to the end of its folder name. WordPress no longer finds the plugin where it expects it and marks it as inactive automatically. Reload the site, it should open right away.
Rename the whole plugins directory to plugins-off and load the admin once, which marks every plugin inactive. Then restore the directory name. The plugins stay inactive, and you can enable them one at a time from the admin. The one that takes the site down again is the guilty one.
Renaming a folder deletes nothing. The plugin settings live in the database and they survive, so you can bring the plugin back with a fixed version without configuring everything again. Deleting, on the other hand, usually takes the settings with it.
A plugin rarely takes a site down for no reason. The usual background causes are a PHP version that is too old, two plugins doing the same job, and a memory limit being reached. The error log tells you which, and reading the log is covered in our guide on a critical error on the site. Changing the PHP version is covered in our guide on changing the PHP version.
Then the plugin was not the cause. Try the same trick on the theme by renaming the active theme folder, which makes WordPress fall back to a default theme. If that does not help either, see the white screen and the 500 error.
Do not reinstall the plugin before you know why it crashed, because the same version crashes the same way. Take a backup before you move folders around, see our guide on backing up a site.
We disable the plugin that crashes, bring the site back and work out which was the cause, the plugin itself or the environment it no longer fits. After that we also know whether it can safely be used again.
