Have you set up a wireless network and does the computer have a wireless card that is enabled and drivers loaded ?
If you go to a computer that is currently connected to your wireless network and open the control panel. Select Network and Internet and then select Homegroup , then select Print and View the Homegroup Password. The next page will have your wireless network password.
If you need the wireless security key then you need to go into the routers internal settings and under wireless and wireless security you will see your wireless security key.
So it will depend on how you have set up your wireless network that you need the Homegroup password or the wireless security key.