Hey there harishkannan97,
It sounds like you are unable to use your iPod Nano with Windows 7 because the device driver will not install. I recommend uninstalling iTunes in the order outlined in this article:
Removing and reinstalling iTunes and other software components for Windows Vista, Windows 7, or Windows 8
http://support.apple.com/kb/ht1923
Then install after following the steps in this article:
Issues installing iTunes or QuickTime for Windows
http://support.apple.com/kb/ht1926
Thank you for using Apple Support Communities.
Cheers,
Sterling