Welcome to the forums!
The G75VW supports both Win7 and Win8, so you should be able to use the keyboard backlight in Win7 too and it works in my Win7 G75VW unit.
If necessary, you can find all the G75VW Win7 drivers at the
ASUS Download site here.
1. When you press other Fn keys like Fn+F5/F6 do you see an onscreen display that shows the screen brightness level?
2. Which ATK package version do you see installed under add/remove programs?
3. Do you see any unknown devices in your device manager?
Good luck!