That Sign-in is for the now obsolete Adobe Photoshop.com Web site. The Plus version of that did have some additional Functional Content, but the Web site has been taken down.
For some of the aspects of Photoshop.com have been rolled into Adobe Revel, but it does not have the extra Menus, Themes, etc., of the old Photoshop.com Plus membership.
Before getting too far into this, are you trying to download and install the photoshop.com plus members only templates or all the Content for Premiere Elements 10, including all the non photoshop.com plus members ones?
For now I am assuming you want all...non photoshop.com plus members only AND photoshop.com plus members only.
Forget about the photoshop.com plus members only...they are gone for your version. Currently they are included as part of the Premiere Elements 11 and 12 versions and are obtained by 11 and 12 users from within the 11 and 12 projects.
Assuming you are after the "regular" Content download for Premiere Elements 10....
Are you trying to start the process from within the open Premiere Elements 10 project. If so, do not.
Please read my blog post how to download Content for 10 and earlier versions.
Use the links and information in the blog post for your task.
Please review. If any questions or need clarification on anything written, please do not hesitate to ask.