This question has been answered by multiple community members. See the first response.
UPDATE modx_users SET hash_class = 'hashing.modMD5', password = MD5('the-new-password') WHERE username = 'theusername';
If the setup directory was transferred, go to yoursite.com/setup and follow the steps. Don't proceed unless the "Upgrade Install" box is checked.
In that case, I'd suggest checking the paths and URLs in these files:
core/config/config.inc.php
manager/config.core.php
connectors/config.core.php
If you can access the DB, look at the modx_users table and see if the default admin user is there with the ID of 1 who is active. If not, you can add one and use Treigh's trick above.