i didn't found product key

BelarcAdvisor has been the most reliable programme for this purpose since Windows XP was a kid. Be careful where you download it from - MajorGeeks is still quite safe.

Sorry, elinaw, your link looks a bit Spammy for our liking.
 


Depending on which OS it is, it may not be "printed" anywhere.

Which OS, and why do you need it?
 
The same applies to a fresh installation and I've done it dozens of times If it was a valid, activated system, so will be a new one of the same version.