That “ridiculously expensive software” has served you quite well considering the fact that it is now 6 versions out of date.
It was released well before Windows 8.1 and is unsupported. You cannot move to a new operating system in a vacuum.
I’m sorry, but you’re on your own here.
Activation status wouldn't affect whether the installer runs...
Run the cleaner tool to remove any traces of the failed install: CS Cleaner Tool for installation problems | CCM, CS6, CS5.5, CS5, CS4, CS3
Run MSconfig to do a clean boot by turning off all non-essential startup programs and services (including anti-virus and malware scanners, third-party firewalls, browser helpers, etc) the re-run the installer (in compatibility mode, if you can).
thanks, peter, for the suggestions. maybe i'll get lucky.