try and see if any of these helps:
1. check if the info in your wp-config.php is current
2. 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. If that resolves the issue, reactivate each one individually until you find the cause.
3. If that does not resolve the issue, try switching to the Default theme. If you don't have access to your admin panel, access your server via FTP or SFTP, 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.
4.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 FTP or SFTP and rename the .htaccess file. If you can't find a .htaccess file, make sure that you have set your FTP or SFTP client to view invisible files.