We are not PMI, so your username for this website will not work on the PMI website! You have to become a member of PMI, pay the membership fee, and then PMI will give you your own username and password.
The PMI membership fee is $129 per year. That seems like a lot, but you will save money on your PMP exam. Here is how from an article that I wrote:
If you are not already a member of the Project Management Institute (PMI), join. You are not required to be a member of PMI to take the PMP® Exam, but being a member can lead to substantial savings. The cost of membership is only $129 USD plus a $10 USD application fee, which is negligible compared to the savings you can see. First, you will receive a member discount of $150 USD for the PMP® Exam. Second, you will have access to resource material at a reduced cost or even free. As a member of PMI you will have access to a free PDF copy of “A Guide to the Project Management Body of Knowledge (PMBOK® Guide)”, a savings of around $40 to $50 USD. Third, as a PMI member you will have access to PMI eReads which contains several PMP® prep books that you can read online at no cost.
So my recommendation: Become a PMI member and get all these discounts. You pay $139 but your discount is at least $190 for your PMP exam and PMBOK Guide.