If you are having any trouble logging into the Download Center, the solution is usually that the user needs to create an account. Even if you think you created an account already, please try going to the Download Center and click on the New User tab (see screenshot below). Using your organization's email address, create a password and click the Sign Up button to see if that logs you in.
If you still cannot login to the Download Center, please see the following list of Common Login Problems and Solutions or create a ticket with Support to get further assistance.