BuddyPress.org

Your best bet is to delete /plugins/buddypress/ and then visit yoursite.com/wp-admin/plugins.php. Then change the theme back to the WordPress default (Kubrick).

You can then reinstall BuddyPress and reactivate the BuddyPress theme. You won’t loose any of your BuddyPress database data doing this, though I recommend making a backup of your database with phpMyAdmin as a matter of good practice.