How do i get the original software back?

Okay, so when i bought my laptop my dad put the windows 7 professional software on my hp pavilion dv6000. unfortunately the windows 7 software stopped being active and now i have to enter some code in order for me to have the full effect of the software. well im selling the laptop and im curious to know if there is any way to reset my laptop back to the original software or are there codes i can download or find to activate windows 7. i would really appreciate anyones help.

HP 625 Notebook AMD V Series V160(2.40GHz) 15.6" 2GB Memory DDR3 1066 320GB HDD 5400rpm DVD Super Multi ATI Radeon HD 4200

HP ProBook 6550b Notebook Intel Core i3 370M(2.40GHz) 15.6" 2GB Memory DDR3 1333 320GB HDD 7200rpm DVD Super Multi Intel HD Graphics

HP ProBook 4525s NoteBook AMD Phenom II Dual-Core P650(2.6GHz) 15.6" 4GB Memory DDR3 1066 500GB HDD 7200rpm DVD Super Multi ATI Radeon HD 4250

HP ProBook 6550b Notebook Intel Core i5 460M(2.53GHz) 15.6" 4GB Memory DDR3 1333 320GB HDD 7200rpm DVD Super Multi Intel HD Graphics