Hello,
Sorry to hear you are having trouble.
The error, and fix noted here:
https://forums.galciv3.com/486732/galactic-civilizations-iii-support-faq
-'Environment Variable Missing Path'
If that fails, has the game ever run? If it has in the past, what can you think of that has changed?
If you try to run the game under a new Windows Admin (<--important) account, does it run then?
Sean Drohan
Stardock Support Manager