Hmmm, I think I would uninstall it completely, also make sure hidden files are visible and look in program data folder, delete the hidden reiza folder in there (even if it seems to be empty).
Then TURN OFF any antivirus completely. GSC does not install well with an AV running. (you should be able to turn it back on after it is installed but I would test the game first).
When you reinstall, DO NOT use c:\programfiles\ or c:\programfilesx86.
Instead, use c:\GSC or C:\Games, anything but program files folder. This will help remove permission problems.
Hopefully it will install properly if you do these things.
