I would like to inform you that if you have purchased Windows 8 Professional under upgrade Offer, then whenever you reformat your system or reinstall on different PC you need to first install Windows XP, vista or Windows 7 then only you can upgrade to Windows 8 Professional and activate Windows 8 Professional.
To download Windows 8 upgrade version please visit the below mentioned link.
Upgrade Windows with only a product key - Windows Help
In order to activate Windows 8 Professional, you have to contact our Product Activation Team and they will activate your product over the phone. You can contact them at the below numbers:
Tel: 080-40103000
Toll free: 1-800-11-1100(BSNL and MTNL)
Toll free: 1-800-102-1100 (AIRTEL
I request you to please choose the IVR option 1 and 1-4 to reach the Product Activation Team.