The webpage shows "Click here to go to our application if the web browser does not redirect you automatically", and you are not invited to enter your PIN.
Depending on the browser, additionaly, a warning "isabel.eu does not respond" and a button "Recover webpage" could be shown.
After each step try to connect with Isabel 6.
Remove all of your Isabel certifcates:
Start Isabel 6 and try to login.
Verify if the websites of Isabel 6 and/or eGovernment websites are available in your list of Trusted Sites.
Make sure you have installed the latest security patches in Windows and verify the following settings in Internet Explorer: