Migration to new server - "The requested page "/" could not be found."
Make sure you have migrated Drupal correctly and all of the non-CiviCRM portions of the site function correctly. 


Sometimes the .htaccess file doesn't get transferred with FTP and
it is an important file.  
Also, migrate the same filesystem/version
from one server to the other, and be sure to upgrade as needed to
keep things secure (either before or after the migration).


At that point if Drupal is working correctly you can focus on CiviCRM.