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That is going to require Microsoft's intervention to get you back up and running. Here is the contact link for them:
Contact Us
Hi anand; try this, it worked for me,and don't forget to make a win7 system image and system repair disks in case you have a problem with win7.
https://www.magicaljellybean.com/keyfinder-faq/
Also note that OEMs use cloned HDDs from a master copy and the Product Key embedded in the Registry will frequently not be the same as on the COA/Certificate Of Authenticity sticker. I have experienced that using the Product Key on the sticker required contacting the OEM instead of Microsoft, apparently one of the things in the licensing agreement between OEMs and Microsoft.