Hi @Yvonne233, regarding the Wordpress login, could you please provide a bit more information on that. What do you do and what exactly do you see after you do it? E.g. do you try to open the wp-login.php page and that fails? Or can you see the login page and enter your credentials, but the login fails? What error message do you see when it fails?
Regarding the error 500 on accessing the Plesk panel, we'd also need a bit more information. Normally Plesk shows a screen with some error details on such an error. Could you please post the screen content (or the details shown)?