Unable to Access Dashboard

Internal server errors (error 500) are often caused by plugin or theme function conflicts, so if you have access to your admin panel, try deactivating all plugins. If you don’t have access to your admin panel, try manually resetting your plugins (no Dashboard access required). If that resolves the issue, reactivate each one individually until you find the cause.

If that does not resolve the issue, try switching to the Twenty Sixteen theme to rule-out a theme-specific issue. If you don’t have access to your admin panel, access your server via SFTP or FTP, or a file manager in your hosting account’s control panel, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the default theme to activate and hopefully rule-out a theme-specific issue.

If that does not resolve the issue, it’s possible that a .htaccess rule could be the source of the problem. To check for this, access your server via SFTP or FTP, or a file manager in your hosting account’s control panel, and rename the .htaccess file. If you can’t find a .htaccess file, make sure that you have set your SFTP or FTP client to view invisible files.

If you weren’t able to resolve the issue by either resetting your plugins and theme or renaming your .htaccess file, we may be able to help, but we’ll need a more detailed error message. Internal server errors are usually described in more detail in the server error log. If you have access to your server error log, generate the error again, note the date and time, then immediately check your server error log for any errors that occurred during that time period. If you don’t have access to your server error log, ask your hosting provider to look for you.

Ok, now from Appearance -> Themes -> Add New, install and activate the Twenty Sixteen theme.

Are you still able to access the Dashboard, and can you view your site?

Ok, so whatever the problem was originally, it was definitely the theme.

Is the old theme still safely as Tempera.hold? If so, you can install a new copy of Tempera from Appearance -> Themes -> Add New.

If that one triggers the same problem, delete the new copy manually, stick with Twenty Sixteen for now, and report the problem to https://wordpress.org/support/theme/tempera

Ok, so if you manually remove that again, you’ll be back with Twenty Sixteen.

Next, I recommend reporting the issue at https://wordpress.org/support/theme/tempera#postform so the theme’s developers and support community can help you with this.