login.php error 404 after changing webhosting provider

I’M sorry but I’m not a web developper at all, I know how to program basic stuff but not much more.

I got a new client that need hosting service and didn’t know she was using wordpress.
She send me a zipped website and a sql database.

I uploaded the website and created and uploaded the database.

Went to the config.php file and change the dbname dbuser dbpassword and dbhost
dbhost i put back localhost.

since then website work fine I can access all the menu except

I’m unable to access the admin page or login page
it show page error 404 unknown page.

I read about 200 topic on it in the forum and can’t find any to help me or that I understand.

Any one can point me in the right direction

Thank you

Maxence