I am using the correct password and username but I am unable to login.
There could be many reasons you are unable to login. First off, you can make sure that you are using the correct username and password. You can have the password emailed to you by using the "Forgot Password" link on the login page.
If you have that information correct, then chances are that the cookies on your browser are disabled. You can verify that by using this Browser Information Tool and check for the result corresponding to "cookies" tag. If it says, "supported" that means the cookies on your browser are enabled. Otherwise, you may need to enable them.
You can follow these steps to enable the cookies:
Click on Tools -> Internet Options -> select "Privacy" tab -> click on "Advanced" tab -> Select "Accept" for both First-Party Cookies and Third Party cookies
Click on Tools -> Options -> Privacy -> check the box for Accept cookies from sites