Product key [$winnt$.inf]

Manual Retrieve Product Key for Windows XP and Windows 2000 from $WINNT$.INF file

$WINNT$.INF located in \Windows\System32 folder is the file that used by Windows installer to perform unattended or automated installs of Windows NT, 2000 or XP. If the file exists, and you have the administrative rights to access the file, the Windows product key can be found and viewed under the section [User Data] (usually at the top), under the name of ProductKey or ProductID.