I had to rename the wp-content/plugins folder, because I had this error 500 issue, when trying to access the /wp-admin path.
Then I logged in and renamed the wp-content/plugins folder again. Now the plugins won't show up in the plugins admin panel. If I try to re-install a plugin I have already installed, the installation fails with something like "plugin path already exists", which is obvious, because the plugin is already installed.
Any ideas how to fix this?