You currently have Q 2016 for Windows, don't you?
Use the same Intuit ID and password you use for Q 2016.
If you're stumped, contact
Quicken Support via Chat or Phone at http://www.quicken.com/contact-support and request help with retrieving your ID and purchasing.
Scroll down to the blue box at the bottom of the Support webpage for access to Chat or Phone Support.
Please let us know if you were able to get it resolved through Support (or not).