Page not found! after migration

I just migrated my website

Exactly how did you do that?
-or-
What did you actually do or not do while trying to do that successfully?

I transferred the wp directory
i changed the address in the database

After making a database backup, edit ‘pref’ to your own table_prefix and then replace ‘http://www.olddomain.com’ and ‘http://www.newdomain.com’ with your own and run this SQL at phpMyAdmin:

UPDATE pref_options SET option_value = replace(option_value, 'http://www.olddomain.com', 'http://www.newdomain.com') WHERE option_name = 'home' OR option_name = 'siteurl';
UPDATE pref_posts SET guid = replace(guid, 'http://www.olddomain.com', 'http://www.newdomain.com');
UPDATE pref_posts SET post_content = replace(post_content, 'http://www.olddomain.com', 'http://www.newdomain.com');

Doing that should find-and-update all related instances beyond your initial address change.

These need to be prefixed with your own table_prefix:
UPDATE pref_options
UPDATE pref_posts
UPDATE pref_posts

example:
UPDATE wp_options
UPDATE wp_posts
UPDATE wp_posts

That is how SQL will know what table/s to modify.

and where shall I run the commands you gave me? where I find the console on phpMyAdmin??

Yes. Click/select your database in phpMyAdmin, then click the ‘SQL’ button you should see there and then paste your edited code into the SQL box and click “Go” or whatever to run it. You should then almost immediately see a report that will show something like “number of rows affected” at the end of each line.

If you might want to do a little looking beforehand, select your database and then “Search” and “all tables” and then paste in your old URL and “Go” to just see what instances you might discover.

You might try either renaming (to disable and hold as a backup) or deleting your current .htaccess file and then re-saving it (indirectly making a new one) at Dashboard > Settings > Permalinks. Doing that has worked for me a couple of times after moving a database. Beyond that, however, I am out of guesses here other than to look at each page and its slug in the editor and/or to possibly do a delete-and-replace at Dashboard > Appearance > Menus.