Sorry to hear you are having trouble.

You will need to be more specific on what methods you have tried.

Did you try this solution from the Support FAQ?

Error: Could not create your Galactic Civilizations Ill user data folder. 

On Windows 10, go to your 'Windows Defender Settings' --> 'Virus and threat protection --> Ransomware protection --> Turn off 'Controlled folder access'.

Also, try whitelisting the game with any antivirus or such programs installed.

Thank you for your patience and patronage.

Try running the game with a new Administrator account.

Create a new Administrator Account

As a test, create a new Administrator (<--Important) Windows account and try to run the game again: 

http://sd.stardock.com/sean/JingImages/2015-09-23_1527.png 

If that works, for some people, we have seen that permissions for the 'My Games' directory have changed after a Windows 10 upgrade (fresh Windows 10 installs would not have the issue).  If you have recently upgraded to Windows 10, and GC3 will not load \ save \ save your settings changes, please download and run the following: 

http://sd.stardock.com/Support/PermFixer.zip 

If that fails, manually make certain that your 'My Games' directory, under your own Windows user account, has 'Full' permissions (write is the key).