Also, upload your remaining files (not only the login form) from your localhost htdocs folder to your domain’s htdocs folder, and edit the configuration file to include the new database host, database name, username and password.
There was a problem before with the password change function in the client area (or specifically, the hosting platform API which it relied upon).
To fix this, could you please try to use the hosting account password change in the client area to change the password to something new. If you want, you can change the password back afterwards. But that should cause the new password to be applied correctly to the database too.