The Sign In window will ask you for your Username or Customer ID and your Password.  Please note that if you have a Customer ID and have not yet updated your account information, you will be prompted to do so after signing in.

After entering your credentials, click the I'm not a robot checkbox.  Follow the on-screen prompts in the pop-up window and click Verify. This will place a green check in the I'm not a robot box, and you may now click Sign In.  Then, answer your security question and click Continue to complete the sign-in process and access your account.