Each copy of the Windows operating system comes with a product identification license key. The key is sent to Microsoft when the computer searches for the latest update. Only valid license keys can update the operating system. The product identification number is shown in the Windows "System" window. You can open this window from the Control Panel, and you need this key when calling Microsoft for technical support.
Click the Windows "Start" button on your computer. Click "Control Panel" to open the main utility window.
Click the "System" link. This link opens a new window that shows several properties for your computer including the computer name, network type, CPU and memory capacity, and the product activation key.
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Scroll down to the section labeled "Windows Activation." In the "Product ID" line item, your product key is listed.