Question: Why is my Center of Gravity disabled/greyed out on Inventor?
Answer: If your Center of Gravity is disabled/greyed out, this may be caused by the Express Mode feature being activated on your assembly. You can rectify this by clicking on the Load Full button from the ribbon.
By default, when you open an assembly which contains over 500 parts, Express Mode is activated. You can change the number of parts which causes the activation of Express Mode, from the Application Options, Assembly tab and changing the part number. Alternatively you can turn this feature off.