wp-login.php not working after migration

I’ve just migrated my wordpress blog (www.joangg.com) from a CentOS 6 VPS to a Digital Ocean Ubuntu 14.04 droplet (from Plesk to the same version of Plesk (the latest one), using Plesk’s migration tool). The website works fine but if I try to access /wp-admin I can enter the user and the password but then it redirects me to http://www.joangg.com/wp-login.php showing a blank page (if I use IE it says it is an HTTP 500 Internal Server Error).

I used Google to search about this problem and tried some ideas that worked to solve similar problems without success. Rewrite module is enabled, I re-upped the wordpress installation from the code (only keeping /wp-content and /wp-config.php), tried to edit .htaccess adding «DirectoryIndex index.html index.htm index.php» at the beggining…

Any ideas? Thanks