Dropbox 20gb missed

I bought new laptop few months back and it was pre-installed with mcafffe 500 days and dropbox 20gb and some others....thing is i didnt even touch the dropbox 20gb ....and it was also pre-installed windows 8.1

now i shifted to windows 7 ultimte..and after sometime i got interested in dropbox so i downloaded it...but i deservve that 20gb help me how to get it...i read this new partnership with dell and dropbox they give 20gb....mines had it...

please i want the 20gb