Do you have a Pro license? Generic key is not meant for activation purposes. It is just a tool to get the Pro installed, but you still need to use our own license after that to activate.
As far as how you activate, depends on the type of license.
Is this a reinstall? Or first time using the license?
Did you purchase the license from Microsoft, or from third party?
Was home edition activated prior to this?
Did you purchase the full Pro license, or just the upgrade license?