Do you have a serial number that came with the disk? It is a 30 alphanumeric code that is required to complete registration. Today, I completed installation of PM2008 on Windows 10 (64-bit/2020-04 build). Try contacting Stardock Support [https://www.stardock.com/support/].
I had to do some troubleshooting to get it to register with Stardock servers.