What brand of Laptop?
do you have the recovery DVD set ?
For Toshiba , Dell & big laptop manufacturers the Recovery DVD set will install without needing Key
The one on label will differ from the one embedded in registry (as found by Belarc Advisor)
If you do not have the recovery DVD set you will have to buy them from the manufacturers
Which is much cheaper than buying a new Windows DVD
Or did you install Windows from a oem or retail Windows DVD and Windows will not accept the key previously used ?
regards
Mike Barnes