You can backup your current activation in 3 simple steps... and re-activate your windows in that same system using the previous activation...
1.backup %SystemDrive%\Windows\ServiceProfiles\NetWorkService\
AppData\Roaming\Microsoft\SoftwarePlatform\Tokens.dat
2.backup %SystemDrive%\Windows\System32\spp\tokens\pkeyconfig\pkeyconfig.xrm-ms
Note: For 64-bit (x64) OS, %SystemDrive%\Windows\SysWOW64\spp\tokens\pkeyconfig\pkeyconfig.xrm-ms have to be backed up too.
3. Retrieve and record the product key used to install and activate the current Windows 7.. use any product key finder if you don't know the key
4.Reinstall Windows 7 When installation wizard prompts for a product key for activation, leave it blank (do not enter anything).
5.In the newly installed Windows operating system, stop the Software Protection Service in Services.msc or with the following command (run in elevated command prompt):
net stop sppsvc
Navigate to the following folder:
%SystemDrive%\Windows\System32\spp\tokens\pkeyconfig\
Note: In 64-bit (x64) operating system, also perform the action in %SystemDrive%\Windows\SysWOW64\spp\tokens\pkeyconfig\ folder.
Take ownership and give user full control permissions (alternatively add grant full control right click menu item) to pkeyconfig.xrm-ms file.
Delete the original default pkeyconfig.xrm-ms file, and replace with the backup copy.
Navigate to the following folder:
%SystemDrive%\Windows\ServiceProfiles\NetWorkService\
AppData\Roaming\Microsoft\SoftwarePlatform\
Take ownership and give user full control permissions (alternatively add grant full control right click menu item) to tokens.dat file.
Delete the original default tokens.dat file, and replace with the backup copy.
Restart the Software Protection Service in Services.msc or with the following command (run in elevated command prompt):
net start sppsvc
Register the product key for Windows 7 or Windows Server 2008 R2 with the following command (run in elevated command prompt):
slmgr.vbs -ipk xxxxx-xxxxx-xxxxx-xxxxx-xxxxx
Replace xxxxx-xxxxx-xxxxx-xxxxx-xxxxx with the actual product key.
6. Windows will activated instantly, off-line
7.note: if its retail key and oem:coa key it will wrk.. but cant guarantee about oem:slp keys/branded oem laptops... for that for reactivation you will need slic 2.1 , your lptops brand cert file and a oem : slp key accrding to your win 7 version and brand
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btw if you feel problem in file replacing its better to do it from a administrator accnt ,,, to activate admin accnt open a elevated cmd and type :
net user administrator /active:yes
logoff login... do all work from admin account