Does reformatting count as installing on a "new" PC for licensing purposes?

No — as long as it's the same physical machine, reformatting and reinstalling is fully covered by your existing license. It only becomes a new activation if you move the key to genuinely different hardware.

What if I've since replaced the motherboard?

A motherboard swap is treated as new hardware by Microsoft's activation system, even on the "same" PC, and can leave activation in a failed state. See our guide on fixing a Windows key that won't activate for the troubleshooting steps that apply here.

I lost my original product key — can I still reformat?

Yes, as long as the license was linked to a Microsoft account beforehand — just sign in after reinstalling and it reactivates without needing the key at all.

Windows 10: Reformatting Your PC and Reusing Your Product Key

A Windows 10 product key is tied to the PC's hardware, not to a single installation. That means you can reformat, reinstall, and reactivate on the same physical machine as many times as you like — you're never buying a second license just because you wiped the drive.

Before You Start

The same physical PC the key was originally activated on
A backup of any files on the drive you're about to reformat
Your original product key, if the license wasn't linked to a Microsoft account
Bootable Windows 10 installation media (see our clean install guide if you need to create one)

1.Check whether your license is linked

Before reformatting, go to Settings > Update & Security > Activation. If it reads "linked to your Microsoft account," reactivation after reinstall is automatic — you'll just need to sign back in with that account.

If it only shows a generic "Windows is activated" without mentioning an account, keep your original 25-character product key handy, since you'll re-enter it manually.

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2.Back up everything you need

Copy documents, photos, and any files you care about to an external drive or a cloud service. Reformatting erases the entire drive — there's no undo.

3.Reformat and reinstall Windows

Boot from your installation media and follow through Windows Setup as normal, choosing Custom: Install Windows only (advanced) and deleting the existing partitions to fully reformat the drive.

If your license wasn't linked to a Microsoft account, enter the original product key when Setup asks for it.

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4.Reactivate

If your license was linked, sign in with the same Microsoft account once you reach the desktop — Windows recognizes the hardware and reactivates within a minute or two.

If it wasn't linked and you didn't enter the key during Setup, go to Settings > Update & Security > Activation and enter it there instead.

Confirm reactivation

Settings > Update & Security > Activation should show "Windows is activated" shortly after sign-in or key entry. If it's still pending after a few minutes, run the built-in Activation troubleshooter from that same page.

Troubleshooting

Issue	Likely Cause	Fix
Reactivation doesn't happen automatically after sign-in	The PC's hardware ID may not have fully propagated to Microsoft's activation servers yet, or you signed in with the wrong account.	Confirm you're signed in with the exact account the license was originally linked to, then run the Activation troubleshooter from Settings.
"This key has already been used" error when re-entering the key manually	This message is misleading — it usually just means the key is already recognized as belonging to this hardware, which is expected.	Run slmgr /ato from an elevated Command Prompt to force an activation attempt; it typically succeeds despite the earlier message.