The default WordPress theme is displaying for me as well... If it were the site or the server, I would get the same error you are receiving.
What URL are you trying to access @hellosarahlou? If you are trying to access an incorrect URL the 403 forbidden error may display due to permissions/or security reasons. When I go directly to /wp-admin the page redirects, without error, to the default WordPress login page.
Go to /wp-login.php and see if the same happens...
Judith "Do one thing every day that scares you." ~ Eleanor Roosevelt