If you have registered, but your username and password are correct, but you can't log in, you can try the following steps.

Why can't I log in after entering my user name and password correctly, and still stay on the login page?

This is because the default security level of your computer is too high. The modification steps are as follows: Select Tools-"Internet Options-Security-Custom Identification-"cookies in the browser menu bar to enable it.

I hope my answer can help you.