In order to install or reinstall Microsoft Windows you must have access to a Product Key for that version of the operating system. The product key can typically be found on a yellow sticker on the CD case of the installation CD, or on a small Microsoft sticker on the outside of the PC's case (if the OS came preinstalled on the machine). If you no longer have access to the product key then you will effectively "lose" a Windows license if you ever have to reinstall the operating system.
There are several methods you can use to uncover a lost product key for a version of Windows that you currently have installed.
For older versions of Windows you can extract the product key from the Windows Registry. Click Start | Run and then type regedit and click OK.
For Windows 95 and Windows 98, browse to this key:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\ProductID
For Windows NT 4.0, browse to this key:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProductID
Alternatively, there are also some free scripts and freeware software programs that can help you:
- Magical Jelly Bean Keyfinder: This is probably the best tool for this task. In addition to finding and identifying product keys for Windows 95/98/ME/NT/2000/XP, it can also uncover product keys for installed versions of Microsoft Office.
- Windows Key Finders: This is actually a group of tools that can be used for unearthing product keys for different versions of Windows.
- Belarc Advisor: This free utility builds a detailed profile of your installed software and hardware. (As suggested in the discussion thread by ShadyHouse).
Whichever method you use, make sure you write down the product key and put it in a safe place for future reference.