For customers with a Stardock Account:
To view your current activations and which PC they're activated to, click below and login:
https://store.stardock.com/login.aspx?ReturnUrl=/myaccount/products
Once logged in, you can click View Product Keys, example: https://www.screencast.com/t/WOJ1RFNT
Then click Manage: https://www.screencast.com/t/rjRljCyH0wG
A window will then display the requested information: https://www.screencast.com/t/PBbR3uY5LI1T
(From here you can also deactivate the activated PC's)
For customers who used Guest Checkout:
Create an account using the email used for purchase: https://store.stardock.com/createaccount
Then jump above where it says For Customers with a Stardock Account.