My laptop hard drive has died and I am replacing it with a new SSD. I am downloading a tool from Microsoft's website to install Windows 10 on the new drive, but how do I activate it? Windows 10 came with the laptop so I don't have a key stored anywhere except on the completely toast hard drive. And I don't think I had the foresight to link the system to a Microsoft account. Any other way to get the system activated using the original key? The laptop is out of warranty btw.
There is no issuie whatsoever doing this.
Install Windows 10 on the new drive and it will activate automatically.
Windows 10 keeps the license in its licensing server and knows your machine. This method is pretty much made for hard drive (any drive) replacement as one of the most common repair issues.
This should just work for you - I have done this myself on my desktop computer changing from HDDs to SSDs. Good Luck.
If, for whatever reason, you have some difficulty (low probability), click on Activate in Computer Properties and walk through the process.
Note: I assume from the nature of the question that this installation of Windows 10 was OEM (likely) or Retail, but not Enterprise Volume License.