due to multi hard drive failer windows 7 seems to be used in more than - Microsoft Community

using windows 7 on mac using parallel desktop . due several computer , hard failures have had reinstall several times, without option of deleting old .so  wont activate though bought new , have had several years when work ok

had same problem other  software email explaining problem necessary reset .but not microsoft , in fact there seems no method reset if happens 

your option use telephone activation reactivate:

how activate windows 7 manually (activate phone)
 
1) click start, , in search box type:   slui.exe  4
 
2) next press 'enter' key
 
3) select 'country' list.
 
4) choose 'phone activation' option.
 
5) stay on phone (do not select/press options) , wait person activation.
 
6) explain problem support person.
 
http://support.microsoft.com/kb/950929/en-us 

Windows / Windows 7 / Install, upgrade, & activate