You just replaced your PC's hard drive, but now you have to reinstall and reactivate Windows or Office on your new system. How can you do this without the product keys for your software? There are some tricks, but you'll have to use them while your current hard drive is still alive and well.
With Windows 10, the OS should automatically activate as the license is usually digital and doesn't require a product key. But with older versions of Windows and with Microsoft Office, a product key is required. What if you need the key for Windows or Office? You can use a third-party utility to display the keys on your PC before a crash occurs, save those key numbers, and then have them squirreled away just in case.
Okay, so let's first go through the scenarios in which you would or would not need a product key to reinstall and reactivate certain Microsoft software. Windows 10 typically does not require a product key. However, there are exceptions, as described in this Microsoft support document. If you purchased Windows 10 from a retail store or on a new device as opposed to upgrading from a previous version, then you have a product key and would need that to reactivate the OS.
Windows 8.1 and Windows 7 both require a product key for activation as well, as detailed in another Microsoft support document.
And what of Microsoft Office? If you have a subscription to Office 365, you don't need a product key. You just install Office 365 on your new hard drive as part of your subscription (though you might need to contact Microsoft to activate it). If you have a digital or physical copy of Office, any version, you have a product key that would need to be entered.
So, having the product keys for your Microsoft products is generally a good idea. The easiest way to grab those product keys is from the product box or in the case of Windows, from a sticker on your PC itself. But if those avenues aren't accessible, here are two products that can reveal your product keys so you can keep them handy.
1 Belarc Advisor
2 Magical Jelly Bean Keyfinder