New
#11
Unless you are using Recovery Disks that came with a factory installation, you ALWAYS have to insert your Product Key to activate Win7.
It sounds like you may have gotten an illegally cracked DVD which self-activates.
I would go back to the Computer store and ask for the Product Key which should have come with the DVD. If they will not give it to you, and you have purchase receipt, contact MS Customer Service to ask for assistance or contact your local authorities to report theft by fraud.