If you lost, cannot retrieve or forgot where you had stored the product key of your Windows 8.1, Windows 8 or Windows 7 OS, do not despair. I would like to show you a simple solution to extract your product key from the OS installed on your PC without using any third party software.

1. Open Notepad.
2. Copy and paste the following text into the notepad window

   function Get-WindowsKey {
       ## function to retrieve the Windows Product Key from any PC
       ## by Jakob Bindslet (jakob@bindslet.dk)
       param ($targets = ".")
       $hklm = 2147483650
       $regPath = "Software\Microsoft\Windows NT\CurrentVersion"
       $regValue = "DigitalProductId"
       Foreach ($target in $targets) {
           $productKey = $null
           $win32os = $null
           $wmi = [WMIClass]"\\$target\root\default:stdRegProv"
           $data = $wmi.GetBinaryValue($hklm,$regPath,$regValue)
           $binArray = ($data.uValue)[52..66]
           $charsArray = "B","C","D","F","G","H","J","K","M","P","Q","R","T","V","W","X","Y","2","3","4","6","7","8","9"
           ## decrypt base24 encoded binary data
           For ($i = 24; $i -ge 0; $i--) {
               $k = 0
               For ($j = 14; $j -ge 0; $j--) {
                   $k = $k * 256 -bxor $binArray[$j]
                   $binArray[$j] = [math]::truncate($k / 24)
                   $k = $k % 24
               }
               $productKey = $charsArray[$k] + $productKey
               If (($i % 5 -eq 0) -and ($i -ne 0)) {
                   $productKey = "-" + $productKey
               }
           }
           $win32os = Get-WmiObject Win32_OperatingSystem -computer $target
           $obj = New-Object Object
           $obj | Add-Member Noteproperty Computer -value $target
           $obj | Add-Member Noteproperty Caption -value $win32os.Caption
           $obj | Add-Member Noteproperty CSDVersion -value $win32os.CSDVersion
           $obj | Add-Member Noteproperty OSArch -value $win32os.OSArchitecture
           $obj | Add-Member Noteproperty BuildNumber -value $win32os.BuildNumber
           $obj | Add-Member Noteproperty RegisteredTo -value $win32os.RegisteredUser
           $obj | Add-Member Noteproperty ProductID -value $win32os.SerialNumber
           $obj | Add-Member Noteproperty ProductKey -value $productkey
           $obj
       }
   }

3. Save the text above into a file with the ".ps1" extension on the Desktop.
   Bonus tip: To make sure that you saving the file with the ".ps1" extension, you can type its name with double quotes, for example, "GetProductKey.ps1".
   
4. Open the Powershell console as administrator by typing "powershell" in the search box of the Start Menu or right on the Start Screen and then press CTRL+SHIFT+Enter. This will open the elevated Powershell window.
5. Enable the execution of local files which are not digitally signed. This can be done with the following command:

   Set-ExecutionPolicy RemoteSigned

   Press Enter to allow the execution policy to be changed.

6. Now you should type the following command:

   Import-Module C:\Users\Winaero\Desktop\GetProductKey.ps1; Get-WindowsKey

   Note: Change the path to the GetProductKey.ps1 file in the command above, according to the location where you saved it.

7. Voila, you product key is displayed on the screen!

See the following video if you have any questions: